[简答题]简述地层接触关系的类型。

An industrial society, especially one as centralized and concentrated as that of Britain, is heavily dependent on certain essential services: for instance, electricity supply, water, rail and road transport, and harbors. The area of dependency has widened to include removing rubbish, hospital and ambulance services, and, as the economy develops, central computer and information services as well. If any of these services ceases to operate, the whole economic system is in danger.
It is this economic interdependency of the economic system which makes the power of trade unions such an important issue. Single trade unions have the ability to cut off many countries’ economic blood supply. This can happen more easily in Britain than in some other countries, in part because the labor force is highly organized. About 55 percent of British workers belong to unions, compared to under a quarter in the United States. For historical reasons, Britain’s unions have tended to
A. They are equal in size of influence.
B. They are less powerful than ever before.
C. They don’t have enough members.
D. They are not organized efficiently.