阅读文言文，完成各题。

       锲而不舍，朽木不折；锲而不舍，金石可镂。蚓无爪牙之利，筋骨之强，上食埃土，下饮黄泉，用心一也。蟹六跪^①而二螯^②，非蛇鳝之穴无可寄托者，用心躁也。

      【注释】①跪蟹脚。②螯蟹钳。

    Going to work by car is getting more expensive today because the petrol(汽油)is getting more expensive（贵）.People are looking for a cheaper way of transportation and they find out that it is a good choice(选择) to ride bikes to work.More and more return to bikes.

    Children often go to school by bike.But now more people are going to work by bike, too.“The bike is easy to use,”says Molly,“and it is also very cheap. It's a good choice for those who do business（生 意） like me.You can buy thirty bikes for the price of a small car. A bike doesn't use expensive petrol.”

    Mr.Brown goes to his hospital by bike every day. He says,“A bike doesn't cost so much money, and most families can have two or more bikes. Bike riding is good for our health. Today most people get fat because they don't get enough exercise. So I tell all my patients(病人) to buy bikes. Besides, in big cities it's usually quicker to travel by bike than by bus or car. Car drivers can do nothing but get angry when there is a traffic jam（有交通阻塞）.

人口的快速增长是破坏或改变野生生物栖息地和过度利用生物资源的最主要原因。