练习册

  • 练习册
  • 试题
    The fiddler crab (蟹) is a living clock. It indicates the time of day by the colour of its skin, which is dark by day and pale by night. The crab’s changing colour follows a regular twenty-four hour plan that exactly matches the daily rhythm of the sun. Does the crab actually keep time, or does its skin simply answer to the sun’s rays, changing colour according to the amount of light strikes it? To find out, biologists kept crabs in a dark room for two months. Even without daylight, the crab’s skin colour continued to change exactly on time. This characteristic probably developed gradually in answer to the daily rising and setting of the sun, to help protect the crab from sunlight and enemies. After millions of years it has become completely regulated inside the living body of the crab. The biologists noticed that once each day the colour of the fiddler crab is especially dark, and that each day this happens fifty minutes later than on the day before. From this they discovered that each crab follows not only the rhythm of the sun but also that of the tides . The crab’s period of greatest darkening is exactly the time of low tide on the beach where it was cought! 【查看更多】

     

    题目列表(包括答案和解析)

    More jobs ______ the school-leavers in the future.

    　 A. will be supplied with 　 B. will be supplied to　　

    　 C. were to supply to 　   D. are supplied to

    查看答案和解析>>

    I was disappointed with the film . I had expected ______ to be much better.

    A. that      B. this     C. one　 D. it　　

    查看答案和解析>>

    Does ______ matter if he can’t finish the job on time?

    A. this     B. that    C. he    D. it　　　

    查看答案和解析>>

    We’ve a lot of things to do. But _____ we must get some sleep.

    　 A. at first 　 B. at once  C. first of all 　 D. the first thing

    查看答案和解析>>

    The coach, because of the driver’s carelessness, was __________ and crashed over the cliff on such a cold December morning.

    A．in support　　  B．out of control     C．in charge　　 D．at the mercy

    查看答案和解析>>


    同步练习册答案