在某地，有一种蝴蝶，绝大多数都是白翅，但有一变异品种，在翅上有两只类似鹰眼的花纹，后来，由于当地注意保护环境，迁来许多鸟类。数年后，人们发现，这里的蝴蝶几乎都是翅上有鹰眼的，很难找到白翅蝴蝶了。试分析可能原因是什么？
有鹰眼花纹的蝴蝶虽然显眼，但对小鸟来说，是一种警戒色，可防止被小鸟吃，是适应当地环境的一个品种，所以生存并繁衍下来；而白翅蝴蝶大多被鸟发现吃了，不适应环境而被淘汰。
| 从方框里选择正确的短语，并用其正确的形式填空。 | |
2. It happened quite___ but some people take it serious- ly. 3. Hey, your serve is too fast. ___,okay? 4. The children wanted to___ and watch television. 5. Farm workers___ only a small section of the population. 6. He is completely ___and he has to have a complete rest. 7. The prisoners were___ to work in the garden. 8. She soon___ French when she went to live in France. 9. Doing that does not___ but Tom listens to nobody. 10. She___ the date on the cheque. |