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All animals must rest, but do they really sleep as we know it The answer to this question seems obvious. If an animal regularly stops its activities and stays quiet and un moving-if it looks as though it is sleeping—then why not simply assume that it is in fact sleeping But how can observers be sure that an animal is sleeping
They can watch the animal and notice whether its eyes are open or closed, whether it is active or lying quietly, and whether it responds to light or sound. These actors are im portant clues, but they often are not enough. Horses and cows, for example, rarely close their eyes, and fish and snakes cannot close them. Yet this does not necessarily mean that they do not sleep. Have you ever seen a cat dozing with an eye partly open Even humans have occasionally been observed to sleep with one or both eyes partially open. Animals do not necessarily lie down to sleep either. Elephants, for example, often sleep standi
A. spend some time resting
B. close their eyes when sleeping
C. are good sleepers
D. are poor sleepers
[单项选择]All animals must rest, but do they really sleep as we know it The answer to this question seems obvious. If an animal regularly stops its activities and stays quiet and unmoving——if it looks as though it is sleeping——then why not simply assume that it is in fact sleeping But how can observers be sure that an animal is sleeping
They can watch the animal and notice whether its eyes are open or closed, whether it is active or lying quietly, and whether it responds to light or sound. These factors are important clues, but they often are not enough. Horses and cows, for example, rarely close their eyes, and fish and snakes cannot close them. Yet this does not necessarily mean that they do not sleep. Have you ever seen a cat dozing with an eye partly open Even humans have occasionally been observed to sleep with one or both eyes partially open. Animals do not necessarily lie down to sleep either. Elephants, for example, often sleep standing up, with their tusks resting in the fork of a
A. spend some time resting
B. close their eyes when sleeping
C. are good sleepers
D. are poor sleepers