根据上下文填空。

      From London to New York, from Hong Kong to Moscow, subways (地铁) are an i______ (1)

way of transportation. T______ (2) in modern cities is often quite h______ (3), and it can sometimes

t______ (4) hours to cross a busy city in a car or bus. Subways help s______ (5) that problem, since

they don't have to stop at traffic lights, and h______ (6) of people can take a subway train together.

In larger subway systems, such as Mexico City's, there are lines that go far away from the city c______ (7). In this way, people living in the suburbs (郊区) can take a train to work. This r______ (8) the

traffic e______ (9) and leaving a city. It also helps stop air pollution, a big problem in many cities.

Finally, subways are usually c______ (10). Basically, in a city with a subway, everybody wins!