nn请进，指点迷津

jackba8888

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.

题目不是很明白，既然说During sleep, the number of sites to which adenosine is bound decreases. 那么教授为什么会假设it is the cumulative binding of adenosine to a large number of sites that causes the onset of sleep呢， 不是很明白，请高人指点

jackba8888

不要沉掉呀，会的同学进来留个言吧，在此先谢过。

jackba8888

顶起来！