A、Because they have unnoticeable sleeping patterns. B、Because they sleep very little. C、Because they are insensitive. D、Because

Our culture is obsessed with sleep, and the lack of it, yet many of us don’t know some basic facts. As many as 35 million Americans experience chronic insomnia, and yet in 2006 only $20 million was spent on research. In the six years that author, professor and lifelong insomniac Gayle Green spent researching and writing her book "Insomniac". She learned almost all there is to know about sleep and the lack thereof. Here are five common myths about how we get our shut-eye and why:
    1. Humans Need Eight Hours Sleep a Night
    There are many ways of sleeping and few cultures sleep in eight-hour consolidated blocks like we do. Until the industrial era, many Western Europeans divided the night into "the first sleep" and the "second sleep." They’d go to bed soon after dark, sleep for four hours then wake for an hour or two during which they’d write, pray, smoke, have sex or even visit neighbors. In fact, there’s some evidence to suggest that this sleep pattern may be the one most in tune with our inherent circadian rhythms.
    2. Sleep Isn’t Just a Bodily Function
    Sleep is a biological, physiological system, akin to the cardiovascular system, the nervous system and so on. Like any other system, it is highly variable, and it wears out and gets more fragile with age.
    3. Animals Don’t Have Sleep Problems
    Insomnia occurs in animals and insects, too, sort of. Technically, insomnia is defined as a "complaint," and since animals can’t complain, it’s difficult to measure in them.
    4. Falling Asleep Is a Gradual Process Nope
    Instead, for most people, it switches on and off like a light switch. But for insomniacs and narcoleptics, the switch doesn’t work quite well. Instead they inhabit the space in between — never entirely awake, nor entirely asleep.
    5. Sleeping Less Burns More Calories
    In the short term, yes, but sleeping less probably won’t help you lose weight. Lack of sleep suppresses our natural appetite-depressants, while fueling appetite-increasers, often leading to weight gain.
21. According to the talk, approximately how many Americans suffer chronic insomnia?
22. Which of the following can best describe Gayle Green?
23. Which of the following sleeping patterns might be the most in tune with our inherent biological system?
24. According to the talk, why is it difficult to measure insomnia in animals?
25. According to the talk, which of the following is true?