任务一：读下文，了解城市交通

Oneway to travel in many big cities is to take the subway. It is fast, cheap, andalmost always on time, but it is often crowded. Buses can be cheaper but muchslower than the subway. Another inexpensive way to see a city is to ride abike. But for many people, the best way to get around downtown is just to walk.

任务二：讨论并比较下列交通工具

bus	cheap	slow	crowded
bike
subway
air