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¡¡¡¡¡¡¡¡ Most animals have little connection with animals of a different kind, unless they hunt them for food. Sometimes, however, two kinds of animals come together in a partnership which does good to both of them. You may have noticed some birds sitting on the backs of sheep. This is not because they want a ride, but because they find easy food in the parasites ( ¼ÄÉú³æ) on sheep. The sheep allow the birds to do so because they remove the cause of discomfort. So although they can manage without each other, they do better together.
¡¡¡¡¡¡¡¡ Sometimes an animal has a plant partner. This relationship develops until the two partners cannot manage without each other. This is so in the coral (ɺº÷) of the sea. In their skins they have tiny plants which act as " dustmen", taking some of the waste products from the coral and giving in return oxygen which the animal needs to breathe. If the plants are killed, or are even prevented from light so that they cannot live normally, the corals will die.
49. Some birds like to sit on a sheep because ¡¡¡¡¡¡¡¡¡¡¡¡ .
A. they can eat its parasites¡¡
B. they depend on the sheep for existence
C. they enjoy travelling with the sheep
D. they find the position most comfortable.
50. The underlined word "they" in the last sentence of the first paragraph refers to .
A. birds and parasites¡¡¡¡¡¡¡¡¡¡¡¡ B. birds and sheep
C. parasites and sheep¡¡¡¡¡¡¡¡¡¡¡¡ D. sheep birds and parasites
51. It can be learnt from the text that the coral depends on the plant for ¡¡ .
A. comfort¡¡¡¡¡¡¡¡¡¡¡¡ B. light¡¡¡¡¡¡¡¡ C. food¡¡¡¡¡¡¡¡ D. oxygen
52. Which is the best title of this passage?
A. Birds and Sheep¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡¡ B. Birds, Sheep and Parasites
C. A Partnership D. Corals live on plants
A B D C