36. GWD25-Q36
The chemical adenosine is released by brain cells when
those cells are active.
Adenosine then binds to more and more sites on cells
in certain areas of the
brain, as the total amount released gradually
increases during wakefulness.
During sleep, the number of sites to which adenosine
is bound decreases. Some
researchers have hypothesized that it is the cumulative
binding of adenosine to a
large number of sites that causes the onset of sleep.
Which of the following, if true, provides the most
support for the researchers’
hypothesis?
A.
Even
after long periods of sleep when adenosine is at its lowest concen-
tration in the
brain, the number of brain cells bound with adenosine remains
very large.
B.
Caffeine,
which has the effect of making people remain wakeful, is known to
interfere with
the binding of adenosine to sites on brain cells.
C.
Besides
binding to sites in the brain, adenosine is known to be involved in
biochemical
reactions throughout the body.
D.
Some
areas of the brain that are relatively inactive nonetheless release
some adenosine.
E.
Stress
resulting from a dangerous situation can preserve wakefulness even
when brain levels
of bound adenosine are high.
这道题，B 选项当时当成无关飞了，我想问问，是不是因果里面的非A 非B
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发表于 2006-9-6 11:15:00
