In the sea, there are many islands. In its warm waters there are some little ones. We call them Coral Islands.
A coral island is very nice to look at. It looks like a ring of land with trees, grass and flowers on it.
One part of the ring is open to the water. There is a little round lake inside the island. If you look into this lake, you'll see beautiful coral. You may think they are flowers. If you look at a piece of coral, you'll see thousands of little holes in it. In each of those holes, a very small sea animal has lived. These sea animals make the coral.
They began to build under the water. Year after year, the coral grew higher and higher. At last it grew out of the water. Then the sea brought to it small trees and other things. After some years, these things changed into earth. Sometimes the wind brought seeds to the earth. Sometimes birds flew over it and brought seeds to the island. The little seeds grew. In a few years, there were plants all over the islands. In a few more years there were trees growing there.
So you see, these islands were built little by little. The workers were very small. Don't they teach us a lesson? What do you know the lesson is?
48. What does a coral island look like? It looks like .
A. a desert B. a ring of land
C. trees, grass and flowers D. a colourful lake
49. There are sea animals living in the holes of the coral.
A. thousands of B. 1,000
C. quite a few D. only one
50. in the sea.
A. We can see many flowers B. There are lots of big trees
C. There are some coral islands D. The water is always warm
51. How were seeds of trees, grass and flowers mainly brought to the coral islands?
A. Fishes brought them there. B. The water brought them there.
C. People brought them there. D. None of the above. B
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(答案→)B
解析：