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It’s such a mon event that you probably never asked yourself why you sleep. 1 In fact, for sleep researchers, it’s one of the biggest unanswered questions in the field.
Stop and think about it for a second. Why should we sleep? 2 But we sleep every night, even when we have had plenty of rest. There are，no doubt，several different answers to this question, but let’s just consider one general purpose of sleep: _3_ Human beings are creatures that are normally active during daylight hours, when our senses function most effectively. 4 We can’t see objects well, our color vision is entirely lost, and we don’t have the smelling or hearing sharpness of other animals. So it actually does make sense to have us stay where we are during the dangerous period when night-waking animals are walking here and there. And one sure way to make sure we don’t fall down everywhere and get lost or eaten is to have us not move for seven or eight hours, rising again only when the light is back and our survival chances are better.
It’s not the only reason we sleep. _5_ Perhaps even the most important one.A．Is it because we get tired?B．Should that put human beings in a terrible situation?C．But from a scientific point of view, this is far from anordinarymatter.D．But in terms of evolution, it may have been one of the first reasons.E. Furthermore, if you were designing an animal, would you have it e into long periods of unconsciousness every twenty-four hours?
F. Sleep as a survival approach.
G. At night, humans do rather poorly.C
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(答案→)C
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