For as long as humans have raised crops as a source of food and other products, insects have damaged them. Between 1870 and 1880, locusts ate millions of dollars worth of crops in the Mississippi Valley. Today in the United States the cotton boll weevil damages about 300 million dollars worth of crops each year. Additional millions are lost each year to the appetites of other plant-eating insects. Some of these are corn borers, gypsy moths, potato beetles, and Japanese beetles.
In modern times, many powerful insecticides have been used in an attempt to destroy insects that damage crops and trees. Some kinds of insecticides, when carefully used, have worked well. Yet the same insecticides have caused some unexpected problems. In one large area, an insecticide was used against Japanese beetles, which eat almost any kind of flower or leaf. Shortly afterward, the number of corn borers almost doubled. As intended, the insecticide had killed many Japanese beetles. But it had killed many of the insect enemies of the corn borer as well.
In another case, an insecticide was used in Louisiana to kill the troublesome fire ant. The insecticide did not kill many fire ants. It did kill several small animals. It also killed some insect enemies of the sugarcane borer, a much more destructive pest than the fire ants. As a result, the number of sugarcane borers increased and severely damaged the sugarcane crop.
To be sure that one insect pest will not be traded for another when an insecticide is used, scientists must perform careful experiments and do wide research. The experiments and research provide knowledge of the possible hazards an insecticide may bring to plant and animal communities. Without such knowledge, we have found that nature sometimes responds to insecticides in unexpected ways.
21. An insecticide was used in Louisiana to kill the troublesome______.
A. corn borer B. Japanese beetle
B. gypsy moth D. fire ant
22. While it is not directly stated, the article suggests that______.
A. insecticides are not dangerous to any small animals
B. insecticides do not always accomplish their purposes
C. insecticides are no longer being used to kill insects
D. insecticides do no harm to people
23. On the whole, the article tells about______.
A. the appetites of plant-eating insects B. the best way to kill boll weevils C. the dangers in using insecticides D. the best way to grow crops
24. Which statement does this article lead you to believe?
A. All changes are predictable. B. Nothing ever changes in nature.
C. Nature is not always predictable. D. Nature always serves man well.
25. Scientists perform careful experiments and do wide research because______.
A. they must learn to destroy all the insects that we need
B. they must be sure one insect pest is not traded for another
C. research keeps them from inventing new insecticide for the crops
D. research helps them find a way to kill all insects
21. D 22. B 23. C 24. C 25. B
英语口语主题:交际英语热门话题47个(2--介绍)
男生女生:我们可以只当朋友吗?
如何用英语表达“原来啊…”
9句狠话教你怎么用英语让人“滚开”
口语情景对话:走遍美国精选 当仁不让 ACT 3 - 2
实用口语情景轻松学:我怀疑我是否能及格
2011年实用口语练习:“淘金热”
英语口语主题:交际英语热门话题47个(25--竞选和辩论)
如何用英文表达“欣赏,感激”
2011年实用口语练习:今天我做东
如何用英文表达“满意”
2011年实用口语练习:5=击掌?
英语口语-安慰
2011年实用口语练习:英语客套话
2011年实用口语练习:课余阅读
2011年实用口语练习:口语当中的ball
2011年实用口语练习:“锅中的火花”
如何提高英语口语
英文如何表达“拍马屁”或“巴结”
2011年实用口语练习:高铁开通了
2011年实用口语练习:取钱那些事
大运会必备接待口语
2011年实用口语练习:“挑刺儿”
2011年实用口语练习:In the bookstore 在书店里
2011年实用口语练习:Assignment 家庭作业
如何用英文表达“你活该”
2011年实用口语练习:Join a club 社团活动
2011年实用口语练习:当猪飞起来的时候
2011年实用口语练习:歉意如何说出口 1
如何用英语表达“你得减肥了”
不限 |
英语教案 |
英语课件 |
英语试题 |
不限 |
不限 |
上册 |
下册 |
不限 |