Every living thing has what scientists call a biological clock that controls behavior. It tells plants when to (21)________ flowers and insects when to leave the protective cocoon and fly away, and it tells animals and human beings when to (22)________, sleep and seek food. It controls our body temperatures, the (23)________ of some hormones (荷尔蒙) and even dreams.
Events (24)________ the plant and animal affect its actions of some biological clocks. Scientists recently found, for example, that a tiny animal called Siberian hamster(仓鼠) changes the color of its (25)________ because of the number of hours of (26)________. In the short days of winter, its fur becomes white. The fur becomes gray-brown in color in longer (27)________ of daylight in summer.
(28)________ signals control other biological clocks. German scientists found that some kind of internal clock seems to order birds to begin their long (29)________ flight twice each year. Birds prevented from flying become (30)________ when it is time for the trip, (31)________ they become calm 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 internal and external signals.
Scientists say they are beginning to learn (32)________ parts of the brain contain biological 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 (33)________ of some of our actions. Probably there are other cells that control other body activities. Dr. Moorhead is studying (34)________ they affect the way we do our work. For example, most of us have great difficulty if we (35)________ change to different work hours.
(36)________ can take many days for a human body to (37)________ the major change in work hours. Dr. Moore Ede said industrial officials should have a better (38)________ of biological clocks and how they affect workers. He said such an understanding could (39)________ sickness and accidents at work and would help increase a factory's (40)________.
根据句意，生物钟掌控着植物的花期。所给选项中A、B、C三 项词义均符合语境，但B、C两项本就有“开花”之意，其后不与flower搭配形成短语。故本题选A最为合适。
联系语境，可知此处应填一描述人和动物日常作息的动词，排除其他三项，填awaken。
根据句意，生物钟控制着人体荷尔蒙的释放。release释放。 reaction反应。relief减轻。recovery恢复。故本题选B。
该句为段落主旨句，联系下文可知该段主要讲的是一种仓鼠根据接受的光照时长不同而改变自身皮毛颜色的例子。可知外界环境也会影响生物钟。故本题选C。
句意：一种叫西伯利亚仓鼠的小动物会因为日照时间的长短而 改变皮毛的颜色。skin 最常用词，指人的皮肤或动物的皮；也可指水 果、植物和种子等的外皮。leather 通常指经过加工的熟皮，可用于制 作各种皮革制品。fur现多指猫、兔等动物软毛皮，也指其他动物的 毛皮。peel指剩下的或可以剥去的果皮或蔬菜皮。根据常识可知，可以变色的是动物最外层看得见的软毛皮，所以选D(fur)。
联系下文“In the short days of winter, its fur becomes … daylight in summer.”，可知此处填daylight。
联系前文“Siberian hamster(仓鼠)changes the color of its fur because of the number of hours of daylight.”可知此处填hours。
上文讲了外因对生物钟的影响，推测本段应该讲的是内因对生 物钟的影响。而且根据下文“German scientists found that some kind of internal clock seems to order”中的internal一词可知本题选C。
根据句意，鸟儿体内的生物钟能指挥它们进行每年两次的迁 徙。migration迁徙，迁移。immigration移民。emigration移民。故本 题选A。
联系下文，可知此处应填calm的反义词。restless焦躁不安的。 ruthless无情的。annoyed恼怒的。anxious焦虑的。故本题选C。
根据句意，上半句和下半句形成对比，故此处应填表转折的连词but。
根据句意，科学家们开始研究大脑的哪一部分控制生物钟，故此处应填which，其他三项均搭配不当。
联系全文主题“生物钟”，可知该处填timing最为合适。
联系上下文，作者讨论的是生物钟如何影响我们的工作，故此处填how，其他三项均不符合语境。
根据句意，大多数人在改变生活作息后都会感到适应困难，此处填must最为合适，其他三项均不符合语境。
根据句子结构不难看出此处需要补充形式主语it，真正的主语为 后面的“to accept the major change in work hours”。
首先根据词义可排除C项，其次A、C两项在表示“使适应”之意 时均要与介词to搭配，故本题选D。
本句考查固定搭配have better understanding of对……有更好的理解。
diminish指因为不断消耗，在数量方面缓慢减少，也指在素质或 者价值的下降。reduce指人为地使某物在数量或重量方面的减少或降低。decrease指数量上的减少；力量或者强度的减弱。decline (数目、 价格、比率)下降；谢绝，婉言推辞；衰退，衰落。文章提到， Moorhead博士认为遵循人体生物钟可以减少患病和发生事故的几 率，并有助于提高工厂的产量。decrease和后文的increase形成鲜明对 比，故选A。
根据句意，更好地理解生物钟能帮助工厂提高产量。production 产量。productivity生产率。故本题选B。