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2020
年托福阅读模拟试题及答案（卷七）
托福阅读文本：
Aviculturists,
people who raise birds for commercial sale, have
not
yet learned how to simulate the
natural incubation of parrot eggs in the
wild. They continue to look for better
ways to increase egg production
and to
improve chick survival rates.
When parrots incubate their
eggs in the wild, the temperature and
humidity of the nest are controlled
naturally. Heat is transferred from the
bird's
skin
to
the
top
portion
of
the
eggshell,
leaving
the
sides
and
bottom
of
the
egg
at
a
cooler
temperature.
This
temperature
gradient
may be vital to successful hatching.
Nest construction can contribute to
this temperature gradient. Nests of
loosely arranged sticks, rocks, or dirt
are
cooler
in
temperature
at
the
bottom
where
the
egg
contacts
the
nesting material. Such
nests also act as humidity regulators by allowing
rain to drain into the bottom sections
of the nest so that the eggs are not
in
direct contact with the water. As the water that
collects in the bottom
of
the
nest
evaporates,
the
water
vapor
rises
and
is
heated
by
the
incubating
bird,
which
adds
significant
humidity
to
the
incubation
environment.
In artificial incubation programs,
aviculturists remove eggs from the
nests
of
parrots
and
incubate
them
under
laboratory
conditions.
Most
commercial
incubators
heat
the
eggs
fairly
evenly
from
top
to
bottom,
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