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 concentration 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.作者: victoria_cc 时间: 2012-9-10 21:23
这题的确很怪，我猜测是不是adenosine to a large number of sites按照短文讲的应该是wakefulness，但结论却说是causes the onset of sleep，所以就要有东西阻止 the binding of adenosine to sites on brain cells，也就是答案B。不知道我的理解对不对，仅供参考！作者: wintertrain 时间: 2012-9-11 21:38
