The loss of biological diversity has become most spectacularly noticeable in extinction or decline of populations of large and well-known animals.Many animal species have become extinct since the 1700’s, among them the California grizzly bear, the dodo, a

The loss of biological diversity has become most spectacularly noticeable in extinction or decline of populations of large and well-known animals.Many animal species have become extinct since the 1700’s, among them the California grizzly bear, the dodo, and the passenger pigeon.Hundreds of other animal species are threatened.In North America, endangered species include the black-footed ferret, the California condor, the desert tortoise, and the whooping crane.

Most species in danger of extinction anywhere in the world are suffering from the intrusion (侵入) of human beings.The Asian elephant, for example, has become an endangered species due to the expansion of the human population throughout its range in southern Asia.In Africa, the African elephants are being killed off for their tusks.Monkeys and other primates throughout the world are threatened by hunting, capture for medical use, and the destruction of their habitats.And the rhinoceroses, lions, and other large mammals of the African savanna (grassy plains with scattered trees) compete for land and life with some of the most rapidly growing human populations in the world.

The loss of biological diversity is most severe, however, in the tropical rain forests.The forests of the tropics are particularly vulnerable to disturbance because the soils have a low capacity for retaining nutrients.Most of the forests’ nutrient elements are held in the tissues of plants.When loggers and farmers destroy existing plant cover, the nutrients are washed from the land into streams, and the land itself becomes less able to support life.Destruction of these forests destroys the habitat of hundreds, sometimes thousands, of species from such creatures as the howler monkey and indigo macaw, to less visible species of plants, insects, and microbes, many of which are not yet known to science.

1.The author points out that species extinction ().

A.is most noticeable in North America

B.is mainly taking place among large animals

C.quickened with industrialization of the society

D.never took place before the 1700’s

2.Which of the following is NOT mentioned with regard to human intrusion?

A.Elephants are killed off for their tusks

B.Some primates are hunted for medical use

C.Growing human population results in the competition for land and life among animals

D.Men live increasingly on animals as their source of food.

3.The chief cause of the gradual disappearance of biological diversity is ().

A.human cruelty

B.human interference

C.the increase of human population

D.the disappearance of the forests

4.In tropical forests，().

A.animals live a hard life due to competition

B.a lot of species die out for lack of food

C.rains constitute the major threat to species

D.a greater number of animals are yet to be known

5.It can be inferred that species extinction ().

A.proceeds of a faster rate than noticeable

B.is the worst among well-known animals

C.is the most severe in Africa

D.is chiefly due to competition among species