为你解答。

1、Which is the best title for this passage? （D）

D. Serious Problems in Big Cities.

解释：最佳标题是“大城市的问题”。即人口迁移带来的种种难题。

2、Which of the following is true? （A）

A. Big cities are not safe and clean enough.

解释：大城市不是很安全、干净。因为人口过多。

3、In this passage the writer advised people （C）.

C. not to move to a big city without thinking about the problems there.

解释：作者建议人们在迁移去大城市之前，先要考虑那里的问题。