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; others are parasitic diseases. Also, population density produces nervous disorders and even drives animals to mass migrations(移民群),like the lemmings of Norway who plunge（沖入）into the sea.

That predatory population 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 rabbit population had gone up and down.

Sometimes a situation occurs in which the predatory population is reduced to a level below which nature can readily replace. On Valcour Island in Lake Champlain, a costly campaign resulted in the elimination（消除）of predatory animals only to have birds and small animals increase for four years afterward. Then, lacking predator control, nature resorted to disease 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（狐猴）to control rats. The mongooses killed off the rats, kids, puppies, and wildlife. Eventually, food became scarce and the mongoose’s population declines.

1. The fact that the number of predators has much to do with that of other animals 　　  .

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

C.hasn’t been proved yet　　　　　　　　　　　　　　　　　　　　  D.is not important now

2. When predator control fails, nature brings animal population into balance by       .

A. eliminating the number of predators

B.seeking the help of disease to reduce other animals

C.increasing the number of other animals

D.replacing the number of predators immediately

3. When the mongooses killed off the rats they 　　  .

A. became problems themselves　　　　　　　　　　　　 B.ate the sugar crop

C.attacked humans　　　　　　　　　　　　　　　　　　　　   D.had nothing to eat

4. It is implied in this passage that 　　  .

A. sugar planter imported mongooses to control rats

B.man should never kill animals

C.man has complete control over nature

D.to upset the balance of nature can be troublesome

 

答案：1A2B3A4D
解析：

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