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  3. A Biological Clock Every living thing has what scientists call a biological clock that controls behavior. The biological clo

A Biological Clock Every living thing has what scientists call a biological clock that controls behavior. The biological clo

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问题                             A Biological Clock
    Every living thing has what scientists call a biological clock that controls behavior. The biological clock tells【C1】______when to form flowers and when the flowers should open. It tells【C2】______when to leave the protective cocoons and fly away, and it tells animals and human beings when to eat, sleep and wake.
    Events outside the plant and anima【C3】______the actions of some biological clocks. Scientists recently found, for example, that a tiny animal changes the color of its fur【C4】______ the number of hours of daylight. In the short【C5】______of winter, its fur becomes white. The fur becomes gray brown in color in the longer hours of daylight in summer.
    Inner signals control other biological clocks. German scientists found that some kind of internal clock seems to order birds to begin their long migration【C6】______twice each year. Birds【C7】______flying become restless when it is time for the trip,【C8】______they become calm again when the time of the flight has ended.
    Scientists say they are beginning to learn which【C9】______of the brain contain biological clocks. An American researcher, Martin Moorhead, said a small group of cells near the front of the brain【C10】______to control the timing of some of our actions. These【C11】______tell a person when to【C12】______, when to sleep and when to seek food. Scientists say there probably are other biological clock cells that control other body activities.
    Dr. Moorhead is studying【C13】______our biological clocks affect the way we do our work. For example, most of us have great difficulty if we must often change to different work hours.
    【C14】______can take many days for a human body to accept the major change in work hours. Dr. Moorhead said industrial officials should have a better understanding of biological clocks and how they affect workers. He said【C15】______understanding could cut sickness and accidents at work and would help increase a factory’s production.
【C13】
选项 A、how
B、why
C、where
D、what
答案A
解析 studying后面是一个从句作它的宾语，而从句起首处应有个连词。把C或D填入空格，上下文意思不连贯。根据下文的例子，作者讨论的不是生物钟为什么会影响我们的工作，而是生物钟如何影响我们的工作。所以，how是正确的选择。
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