A、Crowded houses. B、Polluted water from factories. C、High crime rate. D、Continual noise. D文中列举了城市生活的四大不利之处：hous-ing，pollution，hi

In the eyes of many people, city life is attractive with all its advantages and convenience, yet they don’t see the other side of the picture. First, with the expansion of the city, housing has become a serious problem for city people. Then there is the problem of pollution. Harmful gases from vehicles and poisonous water from factories pollute our surroundings, and noise continually disturbs your peace and rest and drives you mad. Thirdly, modem city life puts a high pressure upon people, you have to hurry to bump into the flood of people, bicycles, cars, buses... All day long you are under great stress. Fourthly, big cities also cause some social problems, of which high crime rate is the most serious one. People are justifiably in fear of becoming victims of burglaries, robbery, murder and other crimes at any time. The city should find some way or other to cope with all these problems.
16. What may drive city people mad, according to the passage?
17. What are city people constantly in fear of?
18. What is this passage mainly about?