单选题 The role of government in environmental management is difficult but inescapable. Sometimes, the state tries to manage the resources it owns, and does so badly. Often, 41 governments act in an even more harmful way. They actually subside the exploitation and 42 of natural resources. A whole 43 of policies, from farm-price support to protection for coal-mining, do environmental damage and (often) 44 no economic sense. Scrapping them offers a two-fold 45 : a cleaner environment and more efficient economy. Growth and environmentalism can actually go hand in hand, if politicians have the courage to 46 the vested interest that subsidies create.
No activity affects more of the earth"s surface than farming. It shapes a third of the planet"s land area, not 47 Antarctica, and the proportion is rising. World food output per head has risen by 4 per cent between the 1970s and 1980s mainly as a result of increases in 48 from land already in 49 , but also beeause more land has been brought under the plough. Higher yields have been achieved by increased irrigation, better crop breeding, and a 50 in the use of pesticides and chemical fertilizers in the 1970s and 1980s.
All these activities may have 51 environmental impact. For example, land clearing for agricultures is the largest single 52 of deforestation; chemical fertilizers and pesticides may 53 water suppliers: more intensive farming and the abandonment of fallow periods 54 exacerbate soil erosion; and the spread of monoculture and the use of high-yielding varieties of crops have been accompanied by the 55 of old varieties of food plants which 56 some insurance against pests or diseases in future. Soil erosion threatens the productivity of land in both rich and poor countries. The United States, 57 the most careful measurements have been done, discovered in 1982 that about one-fifth of its farmland was losing topsoil at a rate 58 to diminish the soil"s productivity. The country subsequently 59 a program to convert 11 per cent of its cropped land to meadow or forest. Topsoil in India and China is 60 much faster than in America.