单项选择题

Endangered Species 　　Endangered species are plants and animals that are in immediate danger of extinction. Extinction is actually a normal process in the course of evolution. Since the formation of the earth, many more species have become extinct than those exist today. These species slowly disappeared because of change of climate and their failure to adapt to such conditions as competition and predation. Since the 1600s, however, the process of extinction has greatly accelerated as a result of both human population growth and technological encroachment on natural ecology systems. Today the majority of the world’s environments are changing faster than the ability of most species to adapt to such changes through natural selection. 　　Species become extinct or endangered for number of reasons, but the primary cause is the destruction of natural habitats. Drainage of wetlands, cutting and clearing of forests, growth of cities, and highway and dam construction have seriously reduced available natural habitats. As the various surroundings become fragments, the remaining animal population crowd into smaller areas, causing further destruction of natural surroundings. Species in these small “islands” lose contact with other populations of their extinction. 　　Some private and government efforts have been organized to save declining species. Laws were made in some countries in the early 1900s to protect wild animals from commercial trade and killing. International endeavors are shown in the convention on International Trade in Endangered Species, approved by 51 nations. Its purpose is to restrict exploitation of wild animals and plants by regulating and restricting trade in certain species. How effective such laws will be in various countries, however, depends on enforcement and support by the people and the courts. Because of lack of law enforcement, the willingness of some segments of society to trade in endangered species, the activities of people who catch and kill animals illegally and dealers who supply the trade, the future of many species is in doubt in spite of legal protection.