It'searly August and the countryside appears peaceful. Planting has long been finished and thefields are alive with strong, healthy crops. Soybeans and wheat are flourishingunder the hot summer sun and the corn, which was"knee-high by the fourth of July",is now well over six feet tall. Herds of dairy and beef cattle are grazingpeacefully in rolling pastures which surround big, red barns and neat, white farmhouses. Everythingas far as the eye can see radiates sense of prosperity. Welcome to theMidwest-one of the most fertile agricultural regions of the world. Thetranquility of the above scene is misleading. Farmers in the Midwest put in some of thelongest workdays of any profession in the United States. In addition to caring for theircrops and livestock, they have to keep up with new farming techniques, suchas those for combining soil erosion and increasing livestock production. Itis essential that farmers adopt these advances in technology if they want to continueto meet the growing demands of hungry world. Agricultureis the number one industry in the United States and agricultural products are thecountry's leading export. American farmers manage to feed not only the totalpopulation of the United States, but also millions of other people throughout therest of the world. Corn and soybean exports alone account for approximately 75percent of the amount sold in world markets. Thisproductivity, however, has its price. Intensive cultivation exposes the earth to thedamaging forces of nature. Every year wind and water remove tons of rich soil fromthe nation's croplands, with the result that soil erosion has become national problemconcerning everyone from the farmer to the consumer. Each field iscovered by a limited amount of topsoil, the upper layer of earth which is richestin the nutrient and minerals necessary for growing crops. Ever since the firstfarmers arrived in the Midwest almost 200 years ago, cultivation and, consequently,erosion have been depleting the supply of topsoil. In the 1830s nearly two feetof rich, black top soil covered the Midwest. Today the average depth is onlyeight inches, and every decade another inch is blown or washed away. This erosion issteadily decreasing the productivity of valuable cropland. A United StatesAgricultural Department survey states that if erosion continues at its present rate, corn andsoybean yields in the Midwest may drop as much as 30 percent over the next 50years.
From Para. 3, we can learn that ______.
A、American farmers feed almost three quarters of the world population
B、75 percent of corn and soybeans in the world market come from the US
C、American agricultural exports have a share of 75% in the global market
D、corn and soybeans take up about three quarters of American agricultural exports
【正确答案】：D
