But the most spectacular thing about the sea cucumber is the way it defends itself. Its major enemies are fish and crabs， when attacked， it squirts all its internal organs into water. It also casts off attached structures such as tentacles. The sea cucumber will eviscerate and regenerate itself if it is attacked or even touched; it will do the same if the surrounding water temperature is too high or if the water becomes too polluted.

　　1. According to the passage， why is the shape of sea cucumbers important?

　　A. It helps them to digest their food.

　　B. It helps them to protect themselves from danger.

　　C. It makes it easier for them to move through the mud.

　　D. It makes them attractive to fish.

　　2. The fourth paragraph of the passage primarily discusses______.

　　A. the reproduction of sea cucumbers

　　B. the food sources of sea cucumbers

　　C. the eating habits of sea cucumbers

　　D. threats to sea cucumbers existence

　　3. What can be inferred about the defence mechanisms of the sea cucumber?

　　A. They are very sensitive to surrounding stimuli.

　　B. They are almost useless.

　　C. They require group cooperation.

　　D. They are similar to those of most sea creatures.

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