新世界英语剑 7

Test 1 passage 1 let

’

s go bats

Bats have a problem: how to find their way around in the dark. They hunt at night, and cannot use

light to help them find prey and avoid obstacles. You might say that this is a problem of their own

making, one that they could avoid simply by changing their habits and hunting by day.

But the

daytime economy is already heavily exploited by other creatures such as birds. Given that there is

a living to be made at night, and given that alternative daytime trades are thoroughly occupied,

natural selection has favoured bats that make a go of the night-hunting trade. It is probable that the

nocturnal

trades

go

way

back

in

the

ancestry

of

all

mammals.

In

the

time

when

the

dinosaurs

dominated the daytime economy, our mammalian ancestors probably only managed to survive at

all

because

they

found

ways

of

scraping

a

living

at

night.

Only

after

the

mysterious

mass

extinction of the dinosaurs about 65 million years ago were our ancestors able to emerge into the

daylight in any substantial numbers.

Bats have an engineering problem: how to find their way and find their prey in the absence of light.

Bats are not the only creatures to face this difficulty today. Obviously the night-flying insects that

they prey on must find their way about somehow. Deep-sea fish and whales have little or no light

by

day

or

by

night.

Fish

and

dolphins

that

live

in

extremely

muddy

water

cannot

see

because,

although

there

is

light,

it

is

obstructed

and

scattered

by

the

dirt

in

the

water.

Plenty

of

other

modern animals make their living in conditions where seeing is difficult or impossible.

Given the questions of how to manoeuvre in the dark, what solutions might an engineer consider?

The

first

one

that

might

occur

to

him

is

to

manufacture

light,

to

use

a

lantern

or a

searchlight.

Fireflies

and

some

fish

(usually

with

the

help

of

bacteria)

have

the

power

to

manufacture

their

own light, but the process seems to consume a large amount of energy. Fireflies use their light for

attracting mates. This doesn

’

t require a prohibitive amount of energy. A

male

’

s tiny pinprick of

light

can

be

seen

by

a

female

from

some

distance

on

a

dark

night,

since

her

eyes

are

exposed

directly

to

the

light

source

itself.

However,

using

light

to

find

one

’

s

own

way

around

requires

vastly more energy, since the eyes have to detect the tiny fraction of the light that bounces off each

part of the scene. The light source must therefore be immensely brighter if it is to be used as a

headlight to illuminate the path, than if it is to be used as a signal to others. In any event, whether

or not the reason is the energy expense, it seems to be the case that, with the possible exception of

some weird deep-sea fish, no animal apart from man uses manufactured light to find its way about.

What else might the engineer think of ? well, blind humans sometimes seem to have an uncanny

sense of obstacles in their path. It has been given the name

‘

facial vision

’

, because blind people

have reported that it feels a bit like the sense of touch, on the face. One report tells of a totally

blind boy who could ride his tricycle at good speed round the block near his home, using facial

vision. Experiments showed that, in fact, facial vision is nothing to do with touch or the front of

the face, although the sensation may be referred to the front of the face, like the referred pain in a

phantom limb. The sensation of facial vision, it turns out, really goes in through the ears. Blind

people, without even being aware of the fact, are actually using echoes of their own footsteps and

of

other

sounds,

to

sense

the

presence

of

obstacles.

Before

this

was

discovered,

engineers

had

already

built

instruments

to

exploit

the

principle,

for

example

to

measure

the

depth

of

the

sea

under a ship. After this technique had been invented, it was only a matter of time before weapons

designers

adapted

it

for

the detection

of

submarines.

Both

sides

in

the

second

world

war

relied

heavily on these devices, under such codenames as Asdic (British) and Sonar (American), as well

as Radar (American) or RDF (British), which uses radio echoes rather than sound echoes.

The sonar and radar pioneers didn

’

t know it then, but all the world now knows that bats, or rather

natural selection working on bats, had perfected the system tens of millions of years earlier, and

their

‘

< br>radar

’

achieves feats of detection and navigation that would strike an engineer dumb with

admiration. It is technically incorrect to talk about bat

‘

radar

’

, since they do not use radio waves.

It is sonar. But the underlying mathematical theories of radar and sonar are very similar, and much

of our scientific understanding of the details of what bats are doing has come from applying radar

theory

to

them.

The

American

zoologist

Donald

Griffin,

who

was

largely

responsible

for

the

discovery of sonar in bats, coined the term

‘

echolocation

’

to cover both sonar and radar, whether

used by animals or by human instruments.

Test 1 passage 2 making every drop count

The

history

of

human

civilization

is

entwined

with

the

history

of

the

ways

we

have

learned

to

manipulate water resources. As towns gradually expanded, water was brought from increasingly

remote sources, leading to sophisticated engineering efforts such as dams and aqueducts. At the

height of the Roman Empire, nine major systems with an innovative layout of pipes and well-built

sewers, supplied the occupants of Rome with as much water per person as is provided in many

parts of the industrial world today.

During

the

industrial

revolution

and

population

explosion

of

the

19

th

and

20

th

centuries,

the

demand

for

water

rose

dramatically.

Unprecedented

construction

of

tens

of

thousands

of

monumental

engineering

projects

designed

to

control

floods,

protect

clean

water

supplies,

and

provide

water

for

irrigation

and

hydropower

brought

great

benefits

to

hundreds

of

millions

of

people. Food production has kept pace with soaring populations mainly because of the expansion

of artificial irrigation systems that make possible the growth of 40% of the world

’

s food. Nearly

one fifth of all the electricity generated worldwide is produced by turbines spun by the power of

falling water.

Yet there is a dark side to this picture: despite our progress, half of the world

’

s population still

suffers, with water services inferior to those available to the ancient Greeks and Romans. As the

united

nations

report

on

access

to

water

reiterated

in

November

2001,

more

than

one

billion

people

lack

access

to

clean

drinking

water;

some

two

and

a

half

billion

do

not

have

adequate

sanitation services. Preventable water- related diseases kill an estimated 10,000 to 20,000 children

every

day,

and

the

latest

evidence

suggests

that

we

are

falling

behind

in

efforts

to

solve

these

problems.

The

consequences

of

our

water

policies

extend

beyond

jeopardizing

human

health.

Tens

of

millions

of

people

have

been

forced

to

move

from

their

homes---often

with

little

warning

or

compensation---to make way for the reservoirs behind dams. More than 20% of all freshwater fish

species are now threatened or endangered because dams and water withdrawals have destroyed the

free- flowing river ecosystems where they thrive. Certain irrigation practices degrade soil quality