2. 外语
  3. 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

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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】______ .   
【C16】
选项 A、He
B、They
C、It
D、This
答案C
解析 惯用搭配题。我们看到take一词，而且后面又有to do sth. ，因此这个句型应该是：it takes some time to do sth. 。It在本句作形式主语．后文的动词不定式短语才是真正的主语。  
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