【单选题】

Urban life has always involved a balancing of opportunities and rewards against dangers and stress; its motivating force is, in the broadest sense, money. The presence of huge numbers of people inevitably involves more conflict, more traveling, the overloading of public services and exposure to those deviants and criminals who are drawn to the rich pickings of great cities.

As a defense against these developments, city dwellers tend to use various strategies to try and reduce the pressures upon themselves; contacts with other people are generally made brief and impersonal; doors are kept locked and so on. There are other strategies, too, which are positively harmful to the individuals, for example, reducing awareness through drags or alcohol. Furthermore, all these defensive forms of behavior are harmful to society in general. Lack of informal social contact and indifference to the misfortunes of others, are amongst the major causes of urban crime.
Present day architecture and planning have enormously worsened the human problems of urban life. People have been forced to leave their familiar homes, usually to be rehoused in tower blocks which are inconvenient. This destruction of established social structures is the worst possible approach to the difficulties of living in a town or city. Instead, every effort should be made to conserve the human scale of the environment, and to retain familiar landmarks.
According to the article, what is the worst problem facing people living in citiesA．Crime.
B．Finding somewhere to live.
C．Social isolation.
Drags and alcoholism.