12．Cockroaches（蟑螂） are the most unpleasant of all insects．Seemingly large and fast，and they live in the most disgusting conditions．
It's no wonder the first reaction of many to seeing a cockroach is to try to destroy it，and few would drop a tear at the thought of the entire species dying out．
But，of course，things are not so simple．Unpleasant though they are，according to biologists the ill-famed cockroach is essential to the survival of the planet's delicate ecosystem．
According to Srini Kambhampati，professor and chairman of the biology department at the University of Texas，the disappearance of cockroaches would play havoc with the nitrogen cycle．
As a leading expert on roaches，he said："Most cockroaches feed on rotten organic matter，which traps a lot of nitrogen．Cockroach feeding has the effect of releasing that nitrogen （in their waste）which then gets into the soil and is used by plants．In other words，extinction of cockroaches would have a big impact on forest health and therefore indirectly on all the species that live there．"
The professor also warned that the Earth's 5，000to 10，000cockroach species are also an important source of food for many birds and small mammals like mice and rats．
In turn，these killers themselves are food of many other species like cats，wolves and snakes，as well as eagles and other big birds．
Any cut to the number of cockroaches would thus have a harmful effect on the wellbeing of all these species that could have a destroying effect on wildlife across that world．
Of course，there's not much chance of a cockroach extinction level event happening any time soon．Still，although it was once believed that they would be one of the few creatures to survive even a nuclear Third World War，that idea has since been considered untrue．
28．What is the main idea of this passage？A
A．The hated cockroach is essential to the survival of the planet's delicate ecosystem．
B．The cockroach is a harmful species which is expected to die out in the near future．
C．Nobody will feel sad at the fact that the entire species of cockroach is dying out．
D．Let's destroy cockroaches without mercy because they polluted the environment．
29．From what Professor Kambhampati said in Paragraph 5，we can learn thatB．
A．cockroaches eat rotten organic matter to get nitrogen
B．nitrogen can make the soil suitable for plants to grow
C．cockroaches'dying out directly destroy all the species
D．plants benefit from cockroaches'getting into the soil
30．Which of the following belong to"these killers"in Paragraph 7？D
A．Cockroaches．
B．Mice and rats．
C．Cats and wolves．
D．Snakes and eagles．
31．We can infer from the last paragraphs thatA．
A．cockroaches can survive a nuclear war
B．cockroaches might cause a world war
C．cockroaches will never be extinct at all
D．cockroaches also need to be protected．
分析 本文屬于說明文閱讀，作者通過這篇文章主要向我們描述了討厭的蟑螂對這個星球脆弱的生態(tài)系統(tǒng)的生存至關(guān)重要．
解答 28．A．主旨大意題．根據(jù)第三段Unpleasant though they are，according to biologists the ill-famed cockroach is essential to the survival of the planet's delicate ecosystem可知這篇文章的主要思想是討厭的蟑螂對這個星球脆弱的生態(tài)系統(tǒng)的生存至關(guān)重要；故選A．
29．B．細(xì)節(jié)理解題．根據(jù)第五段Most cockroaches feed on rotten organic matter，which traps a lot of nitrogen．Cockroach feeding has the effect of releasing that nitrogen （in their waste）which then gets into the soil and is used by plants可知氮可以使土壤適合植物生長；故選B．
30．D．細(xì)節(jié)理解題．根據(jù)倒數(shù)第三段In turn，these killers themselves are food of many other species like cats，wolves and snakes，as well as eagles and other big birds可知蛇和鷹是蟑螂殺手；故選D．
31．A．推理判斷題．根據(jù)最后一段Still，although it was once believed that they would be one of the few creatures to survive even a nuclear Third World War，that idea has since been considered untrue可知．cockroaches可以在核戰(zhàn)爭中生存下來；故選A．
點評 本文是一篇人物故事類閱讀，題目涉及多道細(xì)節(jié)理解題，推理判斷題，主旨大意題．做題時學(xué)生應(yīng)仔細(xì)閱讀原文，把握文章主要內(nèi)容，聯(lián)系文章上下文內(nèi)容并結(jié)合所給選項含義，從中選出正確答案，一定要做到有理有據(jù)，切忌胡亂猜測．
