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（食肉动物）; others are parasites（寄生虫）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（松鸡）and hares, popular game（猎物）—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(损害)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释。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正确。

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. 这里的long been known意为“很久以来便知道的”。即是选项B的意思。

3.[答案]B

【精析】文章第三段的更后一句话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种方式：其一食肉动物，其二寄生虫，其三是疾病。这里的nature即用的是第三种方式。

4.[答案]C

【精析】第四段结尾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杀了rats后，它们自己的生存也成了问题了。故选C.

5.[答案]C

【精析】文中一开始便提到了自然界的平衡，而文中结尾处举的例子也表明，破坏平衡会造成问题。故选C.