A、 They are dangerous to the health of animals and people.
B、 They can interfere with the ecological balance of the environment.
C、 They kill all the insects including beneficial insects.
D、 Both A and B

【正确答案】 D

【答案解析】解析：第一段提出chemicals的两个问题，即A项和B项。

A、 Governments permitted but not encouraged the use of DDT.
B、 Governments permitted and encouraged the use of DDT.
C、 Governments didn"t permit and encourage the use of DDT.
D、 Governments permitted and encouraged the less use of DDT.

【正确答案】 B

【答案解析】解析：根据录音，政府对DDT的使用是允许和支持的，而且没有数量的限制。

A、 It killed all the harmful insects.
B、 It brought a stop to the damage of crops by insects.
C、 It killed only the beneficial insects.
D、 It failed to solve the problem of insects.

【正确答案】 D

【答案解析】解析：DDT不能杀死所有的害虫，另外，害虫的天敌也被杀死，这导致DDT was not solving theinsect problem。

A、 DDT brought some problems that need to be solved themselves.
B、 DDT brought human beings some health problems that needed to be cured in some other methods.
C、 DDT needed some supplementary medicine to help it take effect.
D、 It was necessary to use less DDT.

【正确答案】 A

【答案解析】解析：DDT的使用带来成效的同时也带来了问题，这些问题需要再次被解决。

A、 Chemicals and environment.
B、 Chemicals and their use.
C、 The history of DDT.
D、 The use of DDT and its result.

【正确答案】 A

【答案解析】解析：本文主要讲了Chemicals和environment之间的关系，DDT是作为论据而说明这一观点。