A、Not comfortable. B、Rather crowded and slow. C、Interval is long. D、Cannot reach suburban areas. B文中提到，公交车的问题是比较拥挤，速度比较慢，因此答案是B

I travel quite a lot in Beijing. I think the underground railway is marvelous. I nearly always travel by tube because it is fast and cheap. But I also like to travel by bike, particularly for short journeys. Beijing’s public transport is quite efficient. You can go almost wherever you like by public transport. Buses usually run at very short intervals. But they are rather crowded and slow, particularly in the rush hour. The roads get very congested and there are traffic jams at busy crossroads. When you are in a hurry, the best way to travel in Beijing is by tube. Taxis get held up in traffic jams and besides, the fares are quite high.
    In China today the most common way of traveling is still by rail, although traveling by car or coach is getting more and more popular. We have almost all the provinces and big cities connected by the railways. There are over 53,000 kilometers of track in China. Rail transport provides a very important service to the public, to industry and commerce. Rail fares are usually lower than airfares. They are almost the same as coach fares, but traveling by train is more comfortable than traveling by car or coach.