【答案解析】{{B}}The Problem of Heavy Traffic{{/B}} With population increasing, the traffic in cities becomes heavier and heavier. Urban people have great trouble going to work or back home. Besides they are more likely to get involved in a traffic accident. To solve the problems, there might be two solutions. The first one is to lay down more roads. By so doing, we can lower the degree of crowdedness in the streets and speed up the flow of traffic. But it will occupy too much land. The second solution is to open up more bus lines. This solution will help to reduce the number of bikes and cars. Unfortunately, it also has a draw back: it will bring inconvenience for those who live or work far away from bus routes. In fact, we can adopt these two solutions at the same time because either has its advantages and disadvantages as mentioned above. Only in this way can we efficiently solve the problem of heavy traffic.