There are four levels of sleep, each being a little deeper than the one before. As you sleep, your muscles relax little by little. Your heart beats more slowly, and your brain slows down. After you reach the fourth level, your body shifts back and forth from one level of sleep to the other.
Although your mind slows down, from time to time you will dream. Scientists who study sleep state that when dreaming occurs, your eyeballs begin to move more quickly (although your eyelids are closed). This stage of sleep is called REM, which stands for rapid eye movement.
(77) If you have trouble falling asleep, some people recommend breathing very slowly and very deeply. Other people believed that drinking warm milk will help make you drowsy. There is also an old suggestion that counting sheep will put you to sleep!
A good title for this passage is ______.
A.Sleep
B.Good Health
C.Dreams
D.Work and Rest
第1题
A.吸附法的设备复杂
B.少用或不用有机溶剂, 吸附与洗脱过程中 pH 变化小, 较少引起生物活性物质的变性失活
C.吸附法的操作十分复杂
D.吸附法比较快速, 许多吸附剂又相当廉价, 所以在大体积料液 (稀溶液) 中 提取含量较少的目的物时具有特殊的优越性
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