uniformly-分离度
Removing Dams
For
nearly a century, two United States governmental
agencies, the United States
Army Corps
of Engineers and the Bureau of Reclamation, have
constructed dams
to store water and to
generate electricity. Building these dams provided
cheap
electricity, created jobs for
workers, stimulated regional economic development,
and allowed farming on lands that would
otherwise be too dry. But not everyone
agrees that big dam projects are
entirely beneficial. Their storage reservoirs stop
the flow of rivers and often submerge
towns, farms, and historic sites. They prevent
fish migrations and change aquatic
habitats essential for native species.
The tide may have turned, in fact,
against dam building. In 1998 the Army Corps
announced that it would no longer be
building large dams. In the few remaining
sites
where
dams
might
be
built,
public
opposition
is
so
great
that
getting
approval
for
projects
is
unlikely.
Instead,
the
new
focus
may
be
on
removing
existing dams and
restoring natural habitats. In 1999 Bruce Babbitt,
then the United
States interior
secretary, said, “Of the 75,000 large dams in the
United States, most
were built a long
time ago and are now obsolete, expensive, and
unsafe. They
were built with no
consideration of the environmental costs. As
operating licenses
come
up
for
renewal,
dam
removal
and
habitat
restoration
to
original
stream
flows will be among
the options considered.”
The first active hydroelectric dam in
the United States to be removed against the
wishes of its owners was the 162-year-
old Edwards Dam, on the Kennebec River in
Augusta, Maine. For many years,
the United States Fish and
Wildlife Service had
advocated the removal of this dam,
which prevented migration of salmon, shad,
sturgeon, and other fish species up the
river. In a precedent-setting decision, the
Federal
Energy
Regulatory
Commission
ordered
the
dam
removed
after
concluding that the environmental and
economic benefits of a free-flowing river
outweighed
the
electricity
generated
by
the
dam.
In
July
1999
the
dam
was
removed
and
restoration
work
began
on
wetlands
and
stream
banks
long
underwater.
The
next
dams
likely
to
be
taken
down
are
the
Elwha
and
Glines
Dams
on
the
Elwha
River
in
Olympic
National
Park
in
the
state
of
Washington.
Built
nearly
a
century
ago
to
provide
power
to
lumber
and
paper
mills
in
the
town
of
Port
Angeles,
these dams blocked access to upstream spawning
beds for six species of
salmon on what
once was one of the most productive salmon rivers
in the world.
Simply
removing
the
dams
will
not
restore
the
salmon,
however.
Where
50-kilogram king salmon once fought
their way up waterfalls to lay their eggs in
gravel beds, there now are only
concrete walls holding back still water and deep
beds of muddy deposits. Removing the
mud, uncovering gravel beds where fish
spawn, and finding suitable salmon
types to rebuild the population is a daunting
task. Congress will have to appropriate
somewhere around $$300 to $$400 million to
remove these two relatively small dams
and rehabilitate the area.
Environmental groups, encouraged by
these examples, have begun to talk about
much more ambitious projects. Four
giant dams on the Snake River in Washington
State, for example, might be removed to
restore salmon and steelhead fish runs to
the
headwaters
of
the
Columbia
River.
The
Hetch
Hetchy
Dam
in
Yosemite
National Park might
be taken down to reveal what John Muir, the
founder of the
prestigious
environmental
organization
Sierra
Club,
called
a
valley
“just
a
s
beautiful
and
worthy
of
preservation
as
the
majestic
Yosemite.”
Some
groups
have even suggested
removing the Glen Canyon Dam on the Colorado
River. In
each of these cases, powerful
interests stand in opposition. These dams generate
low-cost
electricity
and
store
water
that
is
needed
for
agriculture
and
industry.
Local
economies,
domestic
water
supplies,
and
certain
types
of
recreation
all
would be severely impacted by
destruction of these dams.
How
does
one
weigh
the
many
different
economic,
cultural,
and
aesthetic
considerations
for
removing
or
not
removing
these
dams?
Do
certain
interests,
such as the rights of native people or
the continued existence of native species of
fish
or
wildlife,
take
precedence
over
economic
factors,
or
should
this
be
a
utilitarian
calculation
of
the
greatest
good
for
the
greatest
number?
And
does
that number include only humans or do
other species count as well?
Paragraph 1
For nearly a
century, two United States governmental agencies,
the United States
Army Corps of
Engineers and the Bureau of Reclamation, have
constructed dams
to store water and to
generate electricity. Building these dams provided
cheap
electricity, created jobs for
workers, stimulated regional economic development,
and allowed farming on lands that would
otherwise be too dry. But not everyone
agrees that big dam projects are
entirely beneficial. Their storage reservoirs stop
the flow of rivers and often submerge
towns, farms, and historic sites. They prevent
fish migrations and change aquatic
habitats essential for native species.
1.
According
to
paragraph
1,
building
dams
was
beneficial
in
each
of
the
following ways
EXCEPT
?
increasing the
amount of land that could be used for farming
?
strengthening
local economies
?
increasing the availability of low-cost
electricity
?
expanding the aquatic habitats of
native species
Paragraph 2
The tide may have turned, in fact,
against dam building. In 1998 the Army Corps
announced that it would no longer be
building large dams. In the few remaining
sites
where
dams
might
be
built,
public
opposition
is
so
great
that
getting
approval
for
projects
is
unlikely.
Instead,
the
new
focus
may
be
on
removing
existing dams and
restoring natural habitats. In 1999 Bruce Babbitt,
then the United
States interior
secretary, said, “Of the 75,000 large dams in the
United States, most
were built a long
time ago and are now obsolete, expensive, and
unsafe. They
were built with no
consideration of the environmental costs. As
operating licenses
come
up
for
renewal,
dam
removal
and
habitat
restoration
to
original
stream
flows will be among
the options considered.”
2.
According
to
paragraph
2,
the
likelihood
that
new
dams
will
be
built
has
decreased because
?
construction
costs have increased enormously
?
safety
standards have become much higher
?
public
opposition to dam construction has increased
?
at most
suitable sites an existing dam would have to be
removed first
3.
The word
?
unpopular
?
inefficient
?
out of date
?
unnecessary
4.
Paragraph 2
supports which of the following ideas about
operating licenses for
large dams?
?
Since 1999
licenses have been renewed only for small dams.
?
Before 1999,
owners applying for a license renewal were more
likely to have
their applications than
they were after that date.
?
Strong public opposition to their
renewal was common even before 1999, but
it was based on safety considerations,
not on environmental ones.
?
The
environmental
cost
of
dams
has
been
a
minor
consideration
in
license
renewal applications since 1999.
Paragraph 3
The
first active hydroelectric dam in the United
States to be removed against the
wishes
of its owners was the 162-year-old Edwards Dam, on
the Kennebec River in
Augusta, Maine.
For many years,
the United States Fish
and
Wildlife Service had
advocated the removal of this dam,
which prevented migration of salmon, shad,
sturgeon, and other fish species up the
river. In a precedent-setting decision, the
Federal
Energy
Regulatory
Commission
ordered
the
dam
removed
after
concluding that the environmental and
economic benefits of a free-flowing river
outweighed
the
electricity
generated
by
the
dam.
In
July
1999
the
dam
was
removed
and
restoration
work
began
on
wetlands
and
stream
banks
long
underwater.
5.
According to
paragraph 3, why did the United States Fish and
Wildlife Service
want the Edwards Dam
removed?
?
?
?
?
6.
Because the
age of the dam made it unsafe
Because
the dam was negatively affecting various species
of fish
Because the dam had caused
wetlands to form
Because the dam no
longer provided economic benefits
Paragraph
3
suggests
that
one
main
consideration
for
keeping
the
Edwards
Dam was
the electricity it generated
the length of time it had been in
operation
the high cost of removing it
the fact that removing it would set a
bad example
?
?
?
?
Paragraph 4
The
next
dams
likely
to
be
taken
down
are
the
Elwha
and
Glines
Dams
on
the
Elwha
River
in
Olympic
National
Park
in
the
state
of
Washington.
Built
nearly
a
century
ago
to
provide
power
to
lumber
and
paper
mills
in
the
town
of
Port
Angeles,
these dams blocked access to upstream spawning
beds for six species of
salmon on what
once was one of the most productive salmon rivers
in the world.
Simply
removing
the
dams
will
not
restore
the
salmon,
however.
Where
50-kilogram king salmon once fought
their way up waterfalls to lay their eggs in
gravel beds, there now are only
concrete walls holding back still water and deep
beds of muddy deposits. Removing the
mud, uncovering gravel beds where fish
spawn, and finding suitable salmon
types to rebuild the population is a daunting
task. Congress will have to appropriate
somewhere around $$300 to $$400 million to
remove these two relatively small dams
and rehabilitate the area.
7.
According to
paragraph 4, why would removing the Elwha and
Glines dams
not be enough to restore
salmon to the Elwha River?
?
They are not the only dams on the Elwha
River.
?
The
lumber
and
paper
mills
in
Port
Angeles
also
block
access
to
upstream
spawning beds.
?
Too many
species of salmon are competing for survival in
one river.
?
The
dams have left the river’s spawning beds in an
unusable condition.
8.
The word
?
new
?
healthy
?
appropriate
?
similar
Paragraph 5
Environmental groups, encouraged by
these examples, have begun to talk about
much more ambitious projects. Four
giant dams on the Snake River in Washington
State, for example, might be removed to
restore salmon and steelhead fish runs to
the
headwaters
of
the
Columbia
River.
The
Hetch
Hetchy
Dam
in
Yosemite
National Park might
be taken down to reveal what John Muir, the
founder of the
prestigious
environmental
organization
Sierra
Club,
called
a
valley
“just
as
beautiful
and
worthy
of
preservation
as
the
majestic
Yosemite.”
Some
groups
have even suggested
removing the Glen Canyon Dam on the Colorado
River. In
each of these cases, powerful
interests stand in opposition. These dams generate
low-cost
electricity
and
store
water
that
is
needed
for
agriculture
and
industry.
Local
economies,
domestic
water
supplies,
and
certain
types
of
recreation
all
would be severely impacted by
destruction of these dams.
9.
The word
?
impressive but
difficult to achieve
?
dangerous and require considerable
planning
?
complex and unlikely to be complete
?
greatly needed
10.
According
to
paragraph
5,
why
do
environmental
groups
want
the
Hetch
Hetchy Dam removed?
?
To restore
salmon and steelhead runs to the Snake River
?
To allow access
to the headwaters of the Columbia River
?
To increase the
size of Yosemite National Park
?
To restore a
valley to its original beauty
Paragraph 6
How
does
one
weigh
the
many
different
economic,
cultural,
and
aesthetic
considerations
for
removing
or
not
removing
these
dams?
Do
certain
interests,
such as the rights of native people or
the continued existence of native species of
fish
or
wildlife,
take
precedence
over
economic
factors,
or
should
this
be
a
utilitarian
calculation
of
the
greatest
good
for
the
greatest
number?
And
does
that number include only humans or do
other species count as well?
11.
The phrase
?
affect
?
have greater
importance than
?
get included among
?
minimize
12.
What is the role of paragraph 6 in the
passage?
?
To
propose a method for deciding whether a given dam
should be removed
?
To emphasize the complexity of the
issues involved in deciding what should
be done about dams
?
To suggest that
the recent tendency not to build new dams may be
wrong
?
To sum up
the points made earlier in the passage about the
advantages and
disadvantages of
removing dams
Paragraph 4
The
next
dams
likely
to
be
taken
down
are
the
Elwha
and
Glines
Dams
on
the
Elwha
River
in
Olympic
National
Park
in
the
state
of
Washington.
Built
nearly
a
century
ago
to
provide
power
to
lumber
and
paper
mills
in
the
town
of
Port
Angeles,
these dams blocked access to upstream spawning
beds for six species of
salmon on what
once was one of the most productive salmon rivers
in the world.
Simply
removing
the
dams
will
not
restore
the
salmon,
however.
■
Where
50-kilogram king
salmon once fought their way up waterfalls to lay
their eggs in
gravel beds, there now
are only concrete walls holding back still water
and deep
beds of muddy deposits.
■
Removing the
mud, uncovering gravel beds where
fish
spawn,
and
finding
suitable
salmon
types
to
rebuild
the
population
is
a
daunting task.
■
Congress will have to appropriate
somewhere around $$300 to
$$400 million
to remove these two relatively small dams and
rehabilitate the area.
■
13.
Look at the four squares
[
■
] that indicate where the
following sentence can
be added to the
passage.
But
aside
from
the
technical
challenges,
the
project
will
also
pose
a
serious
financial challenge.
Where would the sentence best fit?
14.
Directions:
An
introductory
sentence
for
a
brief
summary
of
the
passage
is
provided
below.
Complete
the
summary
by
selecting
the
THREE
answer
choices that express the most important
ideas in the passage. Some answer
choices do not belong in the summary
because they express ideas that are
not
presented in the passage or are minor ideas in the
passage. This question is
worth 2
points.
Drag your choices to the spaces
where they belong. To review the passage, click
on
View Text
.
Many dams were built in the United
States during the last century, and they
provided a broad range of economic
benefits.
●
●
●
Answer Choices
Until
recently,
the
emphasis
in
dam
building was on the economic benefits
of
low-cost
energy
and
water
that
dams
provided,
but
more
attention
is
now
being
paid
to
the
damage
they
cause.
Environmental groups now have a very
good
chance
of
forcing
the
removal
of two major dams,
the Glen Canyon
Dam on the Colorado and
the
Hetch
Hetchy Dam in
Yosemite.
The
removal
of
dams
remains
controversial
because
of
high
restoration
costs,
loss
of
low-cost
electricity,
and
the
loss
of
water
storage facilities.
Since
the
late
1990s,
the
government
has
stopped
building
large
dams,
instead
focusing
on
removing
existing
dams and restoring
natural habitats.
Until
recently,
the
main
reason
for
removing dams was to
restore salmon
runs,
but
it
is
now
recognized
that
a
more
important
reason
to
remove
dams is that they are no longer safe.
Although
the
U.
S.
government
originally
planned
to
remove
the
Elwha and Glines Dams in Washington,
the enormous expense of removal has
resulted
in
a
postponement
of
this
effort.
Coral Reef Communities
Coral
reefs
are
massive
underwater
structures
made
from
the
hard
limestone
exoskeletons of
thousands of tiny living organisms (coral polyps)
produced one on
top of another in warm,
clear, shallow ocean waters. Living polyps extend
upward
and
outward
from
the
coral
colony
center
and
live
on
top
of
the
old
dead
exoskeletons.
Coral
reef
communities
are
crowded
with
other
animals
representing virtually every major
animal phylum. Space is at a premium on reefs,
corals,
seaweeds
(various
forms
of
algae),
sponges,
or
other
organisms
cover
virtually
every
surface.
Because
both
corals
and
algae
require
light
to
survive,
access to light, like space, is also a
resource subject to competition.
Fast-growing,
branching
corals
can
grow
over
slower-growing,
encrusting,
or
massive
corals
and
deny
them
light.
In
response,
the
slower-growing
forms
can
extend
stinging
filaments
from
their
digestive
cavity
and
kill
their
competitor’s
polyps.
Undamaged
polyps
on
the
faster-
growing,
branching
coral,
however,
may grow very long
sweeper tentacles, containing powerful nematocysts
(stingers)
that
kill
polyps
on
the
slower-growing
form.
The
faster-growing
form
repairs
the
damage
and
continues
to
overgrow
its
competitor.
In
addition
to
sweeper
tentacles and
stinging filaments, corals have several other
mechanisms available
for attack or
defense.
In general,
slower-growing corals are more aggressive than
fast-growing species.
In cases where a
competitor cannot be overcome, however, corals may
survive
by taking advantage of
differences in local habitats. Massive corals are
generally
more shade tolerant and able
to survive at greater depths. Therefore, on many
reefs it is the fast-growing, branching
corals that ultimately dominate at the upper,
shallower
portion
of
the
reef,
whereas more massive
forms
dominate
in
deeper
areas.
Corals also must compete with other
reef organisms, each with its own strategies
for
survival.
Sponges,
soft
corals,
and
seaweeds
(algae)
can
overgrow
stony
corals
and
smother
them.
Algae
are
competitively
superior
to
corals
in
shallow
water
but
less
so
at
depth.
Survival
of
coral
in
shallow
water,
therefore,
may
depend
on
grazing
by
plant-eating
echinoderms
(starfish
and
sea
urchins)
and
fishes.
In
Jamaica,
overfishing
removed
most
of
the
plant-eating
fish
from
coral
reefs. Initially, algal growth was kept
in check by grazing sea urchins, but in 1982, a
pathogen
reduced
the
population
by
99
percent.
Without
grazers,
the
algae
were
able to completely overgrow the coral.
Competition may occur among other reef
communities. Grazing by urchins and
fishes
is
important
in
preventing
seaweeds
from
overgrowing
the
reef.
The
dominant
algae
on
a healthy reef
are usually
fast-growing filamentous forms or
coralline algae, well protected by
calcification (hardening) and the production
of
noxious
chemicals.
These
algae
are
inferior
competitors
to
larger,
fleshier
seaweeds, so
grazing by urchins and fishes on the larger
seaweeds allows these
algae
to
persist.
Grazing
on
plants
is
greatest
in
the
shallow
reef
areas
but
decreases with depth, where lower
temperatures and light reduce algal growth.
The reef is, therefore, a mosaic of
microhabitats with different levels of grazing and
different algal communities.
An additional complexity
arises from the activity of damselfish. Because
they are
territorial, many damselfish
species exclude grazers and other species from
certain
areas
of
the
reef.
Algae
grow
rapidly
in
these
territories,
providing
habitat
for
many
small
invertebrates
but
overgrowing
the
corals.
Branching
corals
tend
to
dominate
in
damselfish
territories
because
they
are
upright
and
faster
growing
than the more massive or encrusting
forms.
Although
less
studied
than
on
rocky
shores,
predation
almost
certainly
has
a
significant
influence
on
the
community
structure
of
coral
reefs.
Fish
and
other
predators may preferentially prey on
such competitors of corals as sponges and
gorgonians,
giving
competitively
inferior
reef
corals
an
advantage
in
securing
space. Many species
of fish, mollusks, and crustaceans also feed
directly on coral
polyps.
Several
surgeonfish
and
parrotfish
may
actually
pass
coral
skeletons
through
their
digestive
tracts
and
add
sediment
to
the
reef.
Both
fish
and
invertebrate corallivores (coral-
feeding organisms) seem to attack faster-growing,
branching
species
preferentially,
perhaps
preventing
slower-growing
forms
from
being
overgrown.
Corallivores,
however,
rarely
ever
completely
destroy
a
coral
colony
except
in
cases
where
tropical
storms
or
humans
have
already
done
severe damage. The fact that almost all
small invertebrates on reefs are so well
hidden or highly camouflaged is another
indicator of how prevalent predation is
on reefs and its importance in
determining reef structure.
Paragraph 1
Coral
reefs
are
massive
underwater
structures
made
from
the
hard
limestone
exoskeletons of thousands of tiny
living organisms (coral polyps) produced one on
top of another in warm, clear, shallow
ocean waters. Living polyps extend upward
and
outward
from
the
coral
colony
center
and
live
on
top
of
the
old
dead
exoskeletons.
Coral
reef
communities
are
crowded
with
other
animals
representing virtually every major
animal phylum. Space is at a premium on reefs,
corals,
seaweeds
(various
forms
of
algae),
sponges,
or
other
organisms
cover
virtually
every
surface.
Because
both
corals
and
algae
require
light
to
survive,
access to light, like space, is also a
resource subject to competition.
1.
According to
paragraph 1, all of the following are true of
coral reefs
EXCEPT
:
?
Coral reefs
grow biggest in the deepest waters of the ocean.
?
The organisms
living around coral reefs compete for limited
resources.
?
There are many different organisms in
coral reef communities.
?
Coral reefs consist of the outer
skeletons of small living organisms.
Paragraph 2
Fast-growing,
branching
corals
can
grow
over
slower-growing,
encrusting,
or
massive
corals
and
deny
them
light.
In
response,
the
slower-growing
forms
can
extend
stinging
filaments
from
their
digestive
cavity
and
kill
their
competitor’s
polyps.
Undamaged
polyps
on
the
faster-
growing,
branching
coral,
however,
may grow very long
sweeper tentacles, containing powerful nematocysts
(stingers)
that
kill
polyps
on
the
slower-growing
form.
The
faster-growing
form
repairs
the
damage
and
continues
to
overgrow
its
competitor.
In
addition
to
sweeper
tentacles and
stinging filaments, corals have several other
mechanisms available
for attack or
defense.
2.
According
to
paragraph
2,
how
do
fast-growing
branching
corals
defend
themselves from
attacks by slower-growing corals?
?
By producing
stinging sweeper tentacles
?
By growing on top of the slower-growing
corals
?
By
blocking the light to the slower-growing corals
?
By destroying
the stinging filament of the slower-growing corals
3.
The word
?
adaptations
?
weapons
?
parts
?
means
Paragraph
3
In general, slower-growing corals are
more aggressive than fast-growing species.
In cases where a competitor cannot be
overcome, however, corals may survive
by taking advantage of differences in
local habitats. Massive corals are generally
more shade tolerant and able to survive
at greater depths. Therefore, on many
reefs it is the fast-growing, branching
corals that ultimately dominate at the upper,
shallower
portion
of
the
reef,
whereas more massive
forms
dominate
in
deeper
areas.
4.
The word
?
naturally
?
eventually
?
quickly
?
clearly
Paragraph 4
Corals also must compete with other
reef organisms, each with its own strategies
for
survival.
Sponges,
soft
corals,
and
seaweeds
(algae)
can
overgrow
stony