单选题 All living things need air to live. People need clean air to breathe. But sometimes people make the air dirty. They drive so many cars that the fumes from the cars pollute the air.
Fumes are made when gasoline is burned. The fumes that come out of cars, buses and trucks can pollute the air.
Environmental engineers are people who work to protect the environment. One of their jobs is to design or plan cars that will not pollute the air. Some time ago environmental engineers designed an object for cars that removes harmful pollution. Now cars are causing less pollution than they once did, because environmental engineers worked hard to protect the environment.

单选题 All living things need air ______.
【正确答案】 C
【答案解析】[详细解答] 空气是生物生存的必要条件，但非充分条件，因此A不准确，B显然不对，C为“用来呼吸”，为正确答案。
单选题 ______ has cleaner air.
【正确答案】 C
【答案解析】[详细解答] 因为废气主要来自于城市，因此乡村应该有清洁的空气。
单选题 Environmental engineers' work is to
【正确答案】 B
【答案解析】[详细解答] 这个题需要一定的分析。环境工程师的工作之一是设计污染小的汽车，但这并不是他们的所有工作。他们只是设计或规划汽车，并非就是汽车生产者，因此正确答案应为B。
单选题 Which is not said that can pollute our air?
【正确答案】 A
【答案解析】[详细解答] 文章通篇仅讲到汽车排出的废气污染空气，没有提到从家里出采的烟尘。因此正确答案为A。
单选题 Why do cars cause less pollution than before?
Because ______.
【正确答案】 A
【答案解析】[详细解答] 现在，汽车排出的废气更少了，这归功于环境工程师们的辛勤劳动。B和C没有提到。