29. C

Dẫn chứng: "Large cities often have problems that small towns and rural areas do not have. Two of the biggest problems are heavy traffic and the pollution that cars create." 

30. B
Dẫn chứng: "As the population of a city increases, so does the number of cars on the road. Cities cannot always improve the number and size of their roads and highways to keep up with the number of cars. The result is traffic congestion, or traffic jams." 

31. D

Dẫn chứng: "As the population of a city increases, so does the number of cars on the road."

32. C

Dẫn chứng: "Pollution causes health problems for the people in cities and also hurts the environment." 

`29`. `C`

`-` Được viết trong câu đầu: Large cities often have problems that...do not have.

`30`. `B`

`-` Được viết trong câu 2 đoạn 2: As the population of a city increases, so does the number of cars on the road

`31`. `D`

`-` Được viết trong câu 2 đoạn 2: As the population of a city increases, so does the number of cars on the road

`32`. `C`

`-` Được viết trong câu cuối của bài văn.