单项选择题

Our Disappearing Wildlife
Animal life first appeared on the earth about 400 million years ago. Through the passing millennia, thousands of animal species have come and gone. Until recently, this process was gradual, the result of changes in climate, in habitat, or in the genes of the animals themselves. But the tremendous expansion of modern civilization now threatens to upset this natural balance, putting unprecedented pressure on the survival of our wildlife.
This imbalance can be traced to many causes. Most arise in the greed and poor planning of people. With each increase in our population, the wilderness areas where the animals live get smaller. The use of pesticides to control injurious insects also harms wild birds and animals. Water pollution kills fish in our rivers and oceans. Hunters have almost exterminated many of the larger animals like the big-horn sheep and the grizzly bear. As a result of this unrelenting pressure, our wildlife is disappearing at the rate of one species or subspecies per year.
Of all the continents, the most drastic reduction in wildlife has occured in North America, where the transition from a rural to a highly industrialized society has been most rapid. Among the victims are birds, mammals, and fish. We will never again see the passenger pigeon or the eastern elk. They have been wiped out. Of many other species, only a few representatives still survive in the wild.
Animals that kill other animals for food are called predators. The predators include the wolf, mountain lion, fox, bobcat and bear. Attack against these animals began with the arrival of the first European settlers, who wished to protect their livestock. Yet every animal, including the predator, has its place in nature"s grand design. Predators help maintain the health of their prey species by eliminating the diseased, young, old, and injured. Predators like the mountain lion and the wolf help to keep the deer herds healthy. Their kill also provides food for scavengers that feed on carrion. Occasional loss of livestock must be weighed against the good these animals do in maintaining the balance of nature.
Overhunting an animal is an obvious form of extermination, but there are more subtle processes that often have the same fatal result. One of these is destruction of habitat. When farmers introduced sheep and cattle to North America, the domestic animals competed with the wild animals for the available grazing land. Animals like the buffalo and the pronghorn antelope, which once roamed the plains in countless numbers, were either killed or pushed off the grasslands.
Pesticides have also taken their toll. In 1947, new chemical poison called DDT was introduced. It proved very effective in controlling insect pests like the potato beetle and the boll weevil. But pesticides, which decompose very slowly, accumulate in animals which feed on pest insects or their predators, and the accumulated poisons attack their nervous systems. Pesticides also interfere with the formation of calcium in birds, which lay eggs with very thin shells or no shell at all. When wildlife fail to reproduce, it isn"t very long before they disappear.
Why should we care about the extinction of these birds and animals The answer is simple enough. Every species that becomes extinct is gone forever. With each departure a small part of the diversity of nature that makes life so interesting is also gone. What has man got to look forward to—endless cities and houses and roads that cross barren country devoid of birds and animals Is that the world we want for ourselves and our children Which of the following is a form of wildlife"s extermination