单选题 For millions of years before the appearance of the electric light, shift work, all night cable TV and the Internet, the Earth"s creatures evolved on a planet with predictable and reassuring 24-hour rhythms. Our biological clocks are set for this daily cycle. Simply put, 9ur bodies want to sleep at night and be awake during the day. Most women and men need between eight and eight and a half hours of sleep a night to function properly throughout their lives (Contrary to popular belief, humans don"t need less sleep as they age).
But on average, Americans sleep only about seven and a half hours per night, a marked drop from the nine hours they averaged in 1910. What"s worse, nearly one third of all Americans get less than six hours of sleep on a typical work night. For most people, that"s not nearly enough.
Finding ways to get more and better sleep can be a challenge. Scientists have identified more than 80 different sleep disorders. Some sleeping disorders are genetic. But many problems are caused by staying up late and sleeping in, by traveling frequently between time zones or by working nights. Dr. James F. Jones at National Jewish Medical and Research Center in Denver says that sleep disorders are often diagnosed as other discomforts. About one third of the patients referred to him with possible chronic fatigue syndrome actually have treatable sleep disorders. "Before we do anything else, we look at their sleep," Jones says.
Sleep experts say that most people would benefit from a good look at their sleep patterns. "My motto (座右铭) is "Sleep defensively"," says Mary Carskadon of Brown University. She says people need to carve out sufficient time to sleep, even if it means giving up other things. Sleep routines—like going to bed and getting up at the same time every day—are important. Pre-bedtime activities also make a difference. As with Elsner, who used to suffer from sleeplessness, a few lifestyle changes—avoiding stimulants and late meals, exercising hours before bedtime, relaxing with a hot bath—yield better sleep.

单选题 What is TRUE of human sleep?

【正确答案】 C

【答案解析】[解析] 此题答案见第二段：But on average, Americans sleep only about seven and a half hours per night, a marked drop from the nine hours they averaged in 1910. What"s worse, nearly one third of all Americans get less than six hours of sleep on a typical work night. For most people, that"s not nearly enough.(但平均起来，美国人每晚仅睡大约7.5小时，比1910年平均9小时的睡眠时间有明显下降。更糟的是，将近1/3的美国人在正常晚班的睡眠时间不足6小时。对大多数人来说，那是很不够的。)故选项C正确。

单选题 For our bodies to function properly, we should ______.

单选题 According to the author, many sleeping disorders are caused by ______.

【正确答案】 C

【答案解析】[解析] 此题答案见第三段的第三、四句：Some sleeping disorders are genetic. But many problems are caused by staying up late and sleeping in, by travelling frequently between time zones or by working nights.(有些睡眠疾患是遗传的，但许多睡眠问题是由熬夜、晚起或是经常跨时区旅行和常上夜班造成的。)该句中所提到的问题均属于“不正常的睡眠习惯”，故选项C正确。

单选题 Which of the following measures can help you sleep better?

【正确答案】 B

【答案解析】[解析] 此题答案见文章结尾作者所提供的如何提高睡眠质量的实例：As with Elsner, who used to suffer from sleeplessness, a few lifestyle changes—avoiding stimulants and late meals, exercising hours before bedtime, relaxing with a hot bath—yield better sleep.(比如艾尔斯纳，过去饱尝失眠的痛苦，现在改变了生活方式——睡前避免喝刺激性饮料，晚餐不要吃得太迟，加上洗一个热水澡——睡眠比以前好多了)。只有选项B(洗热水澡)与原文的内容相符。