下列命题正确的是（  ）

____时

阅读下面短文，掌握其大意，并根据所给字母的提示，写出一个英语单词的完整、正确形式，使短文通顺。

    More and more A____ are going to work by bike. Do you know why more people are riding bikes to work? We can answer the question in d____ ways. First, bikes don't need gasoline(汽油)，so it takes little m____ to use them. S____  a bike doesn't need much space, so it is e____ to find a place for it. And to ride a bike is good for one's h____ .People often d____ their cars to offices or to shops in the past. But now people think riding bikes is a good way of d____ sports. That's w____ more Americans are now riding to work by bike, and they are leaving（把...留下）their o____ cars at home.