Questions 26~30 are based on the following passage. The fiddler crab is a living clock.It indicates the time of day by the color of its skin, which is dark by day and pale by night.The crab's changing color 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 color according to the amount of light that strikes it?To find the reason out, biologists kept crabs in a dark room for two months.Even without daylight the crab's skin color 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 color 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 caught！ 26.The fiddler crab is like a clock because it changes color A.in a regular 24-hour rhythm B.in answer to the sun's rays C.at low tide D.every fifty minutes 27.The crab's changing color A.tells the crab what time it is B.protects the crab from the sunlight and enemies C.keeps the crab warm D.is of no real use 28.When the fiddler crabs were kept in the dark,they A.did not change color B.changed color more quickly C.changed color more slowly D.changed color on the same timetable 989• Questions 26"-'30 are based on the following passage. The fiddler crab is a living clock. It indicates the time of day by the color of its skin , which is dark by day and pale by night. The crab's changing color 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 color according to the amount of light that strikes it? To find the reason out , biologists kept crabs in a dark room for two months. Even without daylight the crab's skin color 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 color 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 caught! 26. The fiddler crab is like a clock because it changes color A. in a regular 24-hour rhythm B. in answer to the sun' s rays C. at low tide D. every fifty minutes 27. The crab' s changing color A. tells the crab what time it is B. protects the crab from the sunlight and enemies C. keeps the crab warm D. is of no real use 28. When the fiddler crabs were kept in the dark , they A. did not change color B. changed color more quickly C. changed color more slowly D. changed color on the same timetable li 污9