The "balance of nature" is not an empty phrase. Nature provides a population to occupy a suitable environment and cuts down surplus population to fit the available food supply. One means of reducing surplus population is predators（食肉動物）; others are parasites（寄生蟲）and diseases. Also, population density produces nervous disorders and even drives animals to mass migrations, like the lemmings（旅鼠）of Norway who plunge into（跳入）the sea.

That predators populations increase to control other animals has long been known. Many years ago, the Hudson's Bay Company records revealed that the fox population went up and down about a year after the rabbit population had gone up and down.

Sometimes a situation occurs in which the predators population is reduced to a level below that which nature can readily replace. On Valcour Island in Lake Champlain(New York), a costly campaign resulted in the elimination of predatory animals only to have birds and small animals—including grouse（松雞）and hares, popular game（獵物）—increase for four years afterward. Then lacking predator control, nature resorted to cut down these populations.

Jamaica had an example of nature's persistence in providing animals for existing habits. Sugar planters, about 75 years ago, imported mongooses to control rats. The mongooses killed off the rats and, with plentiful food, multiplied. Rats became scarce and the mongooses ate lambs, kids, puppies（小狗）, and wildlife. Eventually, food became scarce and the mongoose's population declined.

1. According to the article, the phrase "balance of nature" means ______.

A. the relation of wildlife to man

B. the adequacy of the food supply to support its animal population

C. the ratio of small game to predators

D. the destruction of predators

2. The effect of predator control over other animal populations ______.

A. has just been learned B. is not recent knowledge

C. is not important now D. was learned in Norway

3. When predators control is not available, nature brings animal population into balance by resorting to ______.

A. hunters B. diseases

C. storms and flood D. forest fires

4. When the mongooses in Jamaica killed off the rats, they ______.

A. quickly died for lack of food B. attacked humans

C. became problems themselves D. ate the sugar crop

5. Implied but not stated: ______.

A. Sugar planters imported mongooses to control rats

B. Man should never tamper(損害)with nature

C. To upset the balance of nature can be troublesome

D. Man has complete control over nature

1.[答案]B

【精析】the balance of nature的意思在文中的第二句便作了解釋。The "balance of nature" is not an empty phrase. Nature provides a population to occupy a suitable environment and cuts down surplus population to fit the available food supply.故B正確。

2.[答案]B

【精析】第二段中第一句That predators populations increase to control other animals has long been known. 這里的long been known意為“很久以來便知道的”。即是選項B的意思。

3.[答案]B

【精析】文章第三段的更后一句話Then lacking predator control, nature resorted to cut down these populations.而且在文中的第一段已指出有三種方式：其一食肉動物，其二寄生蟲，其三是疾病。這里的nature即用的是第三種方式。

4.[答案]C

【精析】第四段結(jié)尾The mongooses killed off the rats and, with plentiful food, multiplied. Rats became scarce and the mongooses ate lambs, kids, puppies（小狗）and wildlife.可知mongooses殺了rats后，它們自己的生存也成了問題了。故選C.

5.[答案]C

【精析】文中一開始便提到了自然界的平衡，而文中結(jié)尾處舉的例子也表明，破壞平衡會造成問題。故選C.