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Every living thing has what scientists call a biological clock that controls behavior. It tells plants when to 【C1】______ flower
Every living thing has what scientists call a biological clock that controls behavior. It tells plants when to 【C1】______ flower
admin
2010-12-04
57
问题
Every living thing has what scientists call a biological clock that controls behavior. It tells plants when to 【C1】______ flowers and insects when to leave protective cocoon(茧) and fly away. And it tells animals and human beings when to 【C2】______ , sleep and seek food. It controls our body temperatures, the 【C3】______ of some hormones and even dreams.
Events 【C4】______ the plant and animal affect its actions. Scientists recently found that a tiny animal called Siberian hamster changes the color of its 【C5】______ because of the number of hours of 【C6】______ . In shorter days of winter its fur becomes white. The fur becomes gray-brown in longer 【C7】______ of daylight in summer.
【C8】______ signals control other biological clocks. German scientists found that some internal one seems to order birds to begin their 【C9】______ flights two times each year. Birds prevented from flying become 【C10】______ when it is time for the trip. 【C11】______ they become can again when the time of the flight has ended. A mix of outside and internal events controls some biological clocks;such things as heartbeat and the daily change from sleep to walking take place because of both external and internal signals.
Scientists are beginning to learn 【C12】______ parts of the brain contain the biologicaI clocks. A researcher at Harvard University. Dr. Martin Moore Ede, said a small group of cells near the front of the brain seemed to control the 【C13】______ of some of our actions. Probably there are other cells to control other body activities. He is studying 【C14】______ they affect the way we do our work. Most of us have great difficulty if we 【C15】______ often change to different work hours. 【C16】______ call take many days for a human body to 【C17】______ a major change in work hours. Industrial officials should have a better 【C18】______ of biological clocks and how they affect workers. He said such an understanding could 【C19】______ sickness and accidents at work, and would help increase 【C20】______ .
【C15】
选项
A、may
B、can
C、must
D、might
答案
C
解析
语义衔接题。情态动词的使用应该参照语境。人们更换工作时间一般是迫不得已而为之,因此只有等到必须做的时候才会更换。所以选C.must,表示“必须”。may“可能,也许”;can“能够,可以”;might(may的过去式)“应该,可能”。
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0
大学英语六级
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