标题: 29号考试！求解答！rp感谢 [打印本页] 作者: liyi422 时间: 2010-9-28 00:41 标题: 29号考试！求解答！rp感谢 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