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(细胞)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 ungrowing 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 事实细节题。由第六句可知,如果海蠕虫生活在阴暗的环境,而且没有食物可吃,它们会变得越来越小。故选D。
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