We are used to the idea of aging in ourselves. We are so used to this that it comes as a surprise to find that there may be some

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问题    We are used to the idea of aging in ourselves. We are so used to this that it comes as a surprise to find that there may be some animals that do not age.
   Sea anemones (海葵) are an example. Some have been kept for nearly a century without showing any signs of lifelessness. Some kinds of sea worms can even " grow backwards. " If kept in the dark and given nothing to eat, they get steadily smaller. They finally end as a ball of cells looking rather like the egg from which they came. Under good conditions the ball will turn back to a worm and start growing again. One could probably keep them growing and un-growing again and again.  
Some sea worms grow smaller when they_______.

选项 A、lose weight
B、live in the darkness
C、are under good conditions
D、don’ t eat and are kept in the dark

答案D

解析 从文章第二段“If kept in the dark and given nothing to eat,they get steadily smaller”可知,如果海葵待在黑暗中,并且不吃东西,就会变小。因此选D。
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