[单项选择]Every living thing has what scientists call a biological clock that controls behavior. It tells plants when to (62) flowers and insects when to leave protective cocoon (茧)and fly away. And it tells animals and human beings when to (63) , sleep and seek food. It controls our body temperatures, the (64) of some hormones and even dreams.
Events (65) the plant and animal affect its actions. Scientists recently found that a tiny animal called Siberian hamster changes the color of its (66) because of the number of hours of (67) . In shorter days of winter its fur becomes white. The fur becomes gray-brown in longer (68) of daylight in summer.
(69) signals control other biological clocks. German scientists found that some internal one seems to order birds to begin their (70) flights two times each year. Birds prevented from flying become (71) when it is time for the trip. (72)
A. acknowledgement
B. understanding
C. information
D. knowledge

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