扫描二维码，直接登录
题库 / GMATLA-CR-88
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?
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.
Caffeine, which has the effect of making people remain wakeful, is known to interfere with the binding of adenosine to sites on brain cells.
Besides binding to sites in the brain, adenosine is known to be involved in biochemical reactions throughout the body.
Some areas of the brain that are relatively inactive nonetheless release some adenosine.
Stress resulting from a dangerous situation can preserve wakefulness even when brain levels of bound adenosine are high.
细胞活跃---A就被释放，醒着的时候不断累计增加，增加到一个峰值后，就会导致睡眠，然后睡眠状态这个A又会慢慢减少登录 或 注册 后可以参加讨论
E有因(adenosine is high)无果(not sleep)，削弱.
A与题目说的相反
支持假设→说明大量的结合会引起睡眠or结合被打断会保持清醒。
b,咖啡因打断结合，人们保持清醒。
（Ｂ）咖啡因會阻斷和brain cells的結合，表示確實若沒有咖啡因讓他倆結合會讓人想睡覺，所以ＡＤ太多與啟動睡眠有關
（Ｅ）壓力會使人保持清醒即使腦袋的ＡＤ很高，所以即使ＡＤ很高應該要入睡卻因為壓力而沒入睡，這點out of scope
A 讲的是睡了很长一段时间，与原题不符。
B 咖啡因影响A物质与大脑的接收器的绑定，导致清醒。正确。
以下为无关选项。
C A物质的性质。
D 脑的其他区域。
E 压力的影响。