Big cites today are confronted with very serious problems. Transport is a major difficulty: some planners believe in mass transport system;others believe in making it possible for citizens to move 【C1】______ in private cars. There are several ways of 【C2】______a public transport system. Sometimes it is built under the ground,sometimes it is on the【C3】______,and sometimes it is even above ground level, 【C4】______in parts of New York and more crime and Tokyo for example. In most cases, of course,it is a combination of some or all of these elements. 

The decline of the city centers has also been a problem in the last 30 years. The hearts of many cities have become poorer and poorer, with more and more crime and violence, while the people who can afford to have moved out to the suburbs. This is the opposite of the situation 100 years ago, where wealthy people lived in the center, and the poor lived on the outskirts of the city. 

In order to solve these problems, some planners believe we should limit the size of our cities,perhaps by restricting population,or perhaps by offering attractive jobs in the provinces. Others believe that cities cannot be limited in size and that the problems must be solved in a variety of ways—by creating green areas,building【C5】_____houses for everybody,stopping factory pollution.【C6】______motor transport, and so on.

1. A.outside B.through C.across D.about

2. A.setting up B.building up 

3. A. earth B.surface C.soil D.field

4. A.as B.like C.same D. similar

5. A.fundamental. B.delicate C. eternal D.decent

6. A.developing B. forbidding C.reforming D.eliminating

有些很容易排出的选项我就没打，希望老师给出这几个题的解析，谢谢啦～