阅读下面的短文，从每题所给的四个选项(A、B、C、D)中，选出最佳选项。
Rush hour traffic is a problem in many big cities around the world. Commuters(道勤者)rush to and from their jobs in cars, buses, subways, trains, and even on bicycles. Large cities in the United States have two rush hours—one in the morning and one in the evening. But in cities in other parts of the world, there are four rush hours. In Athens and Rome, for example, many workers go home for lunch and a nap. After this midday break, they rush back to their jobs and work for a few more hours.
In Tokyo, there's a big rush hour underground. Most of the people in Tokyo take the subways. The trains are very crowded. Subway employees called packers wear white gloves and help pack the commuters into the trains when the doors place. They make sure that all purses, briefcases, clothes, and hands are inside the trains.
In Seoul, many computers prefer to take taxis to get to work. To hail_a_cab,_many people stand at crossroads and raise two fingers. This means they'll pay the cab driver double the usual fare. Some people even raise three fingers! They'll pay THREE times the normal rate.
Streets in Rome are very crowded with automobiles and mopeds(摩托自行车)during rush hours. The city can't make its streets wider, and it can't build new highways, because it doesn't want to disturb many historic sites in the city, such as the Forum and the Colosseum. It took the city fifteen years to construct a new subway system. Construction had to stop every time workers found old artifacts and discovered places of interest to archaeologists(考古学家)．
In many big cities, there are special lanes on highways for carpools. These are groups of three or more people who driver to and from work together. They share the costs of gas and parking and take turns driving into the city.
Getting to work and getting home can be difficult in many places around the world. Rush hour traffic seems to be a universal problem.
Big cities have traffic problems during rush hours because there are________.

A．special lanes on highways

B．many commuters

C．four rush hours

D．many cars on the street

Most of commuters in Tokyo________.

A．take subway trains to work

B．are packers

C．take taxis to work

D．carry briefcases to work

To “hail a cab” means to________.

A．pay double the normal rate

B．try to get a cab

C．prefer to take taxis

D．to stand at crossroads

Why did it take a long time to build a subway system in Rome?

A．Because the streets were very crowded.

B．Because there are many historic sites.

C．Because the workers discovered many artifacts and places of interest.

D．Because the traffic always stopped the construction.

Commuters in carpools probably________.

A．live in the city

B．take the subway to work

C．save money on gas and parking fees

D．have special license plates(牌照)