2008年9月20日晚，巴基斯坦首都伊斯兰堡的万豪酒店发生自杀炸弹袭击，至少造成60人死亡，200多人受伤。塔利班宣称对这起袭击事件负责。21日早晨，巴基斯坦总统扎尔达里在对全国发表的电视演说中表示，“巴基斯坦人是勇敢和无畏的人民，恐怖主义是癌症，我们决心终结它”。恐怖主义再次引起国际社会的高度关注，下列对恐怖主义的认识正确的是（ ）

①恐怖主义是当今世界矛盾和冲突的根源 ②恐怖主义是强权政治的新体现 ③反对恐怖主义要发挥联合国的作用 ④恐怖主义对世界和平构成严重威胁

A．①②

B．②③

C．①③

D．③④

It is clear that some chemicals can damage the health of animals and humans. (1) , this is not the only problem that (2) be caused by the careless use of chemicals. Chemicals can also (3) the ecological balance of the environment. If the ecological balance is disturbed, the results can be (4) serious.

The (5) of DDT illustrates the problem. DDT, a chemical which kills insects, at first seemed to be a perfect answer (6) many problems. It would control insects that caused dangerous diseases, (7) insects that caused billions of dollars of damage to crops every year. Governments permitted and even (8) the use of DDT. Farmers in many countries (9) to spray it on their crops. The (10) results were good: Damage to crops (11) down, and profits went up. However, the chemical had effects which the scientists didn’t see in (12) . First, it also killed insects which were the (13) enemies of the harmful insects and which were therefore beneficial to farmers. Second, and perhaps worse, DDT did not kill (14) harmful insect. A few insects had natural resistance to the chemical. They (15) and reproduced in large numbers. In a few years there were large numbers of insects which were not (16) by DDT, and there were (17) insects which could act as natural (18) on these new "super-insects". Finally, it became clear that DDT was not solving the insect problem. In fact, it was making the problem worse. It (19) became necessary to find a second (20) for the effects of the first.

18（）

A.controls 

B.enemies 

C.choices 

D.means