Understanding the TestChoose the best answer for each of the following questions according to the test.Keeping Food on the Table1. It’s early August and the countryside appears peaceful. Planting has long been finished and the fields are alive with strong, healthy crops. Soybeans and wheat are flourishing under 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 grazing? peacefully in rolling pastures which surround big, red barns and neat, white farmhouses. Everything as far as the eye can see radiates4a sense of prosperity. Welcome to the Midwest — one of the most fertile agricultural regions of the world. 2. The tranquility of the above scene is misleading. Farmers in the to Midwest put in some of the longest workdays of any profession in the United States. In addition to caring for their crops and livestock, they have to keep up with new farming techniques,such as those for combining soil erosion and increasing livestock production. It is essential that farmers adopt these advances in technology if they want to continue to meet the growing demands of a hungry world.3. Agriculture is the number one industry in the United States and agricultural products are the country’s leading export. American farmers manage to feed not only the total population of the United States, but also millions of other people throughout the rest of the world. Corn and soybean exports alone account for approximately 75 per cent of the amount sold in world markets.4, This productivity, however, has its price. Intensive cultivation exposes the earth to the damaging fores of nature., Every year wind and water remove tons of rich soil from the nation‘s croplands, with the result that soil erosion has become a national problem concerning everyone from the farmer to the consumer.5. Each field is covered by a limited amount of topsoil, the upper Iayer of earth which is richest in the nutrient and mineralsnecessary for growing crops. Ever since the first farmers arrived in the Midwest almost 200 years ago, cultivation and, consequently, erosion have been depleting the supply of topsoil. In the 1830s, nearly two feet of rich, black top soil covered the Midwest. Today the average depth is only eight inches, and every decade another inch is blown or washed away. This erosion is steadily decreasing the productivity of valuable cropland. A United States Agricultural Department survey states that if erosion continues at its present rate, corn and soybean yields in the Midwest may drop as much as 30 per cent over the next 50 years.6. So far, farmers have been able to compensate for the loss of fertile topsoil by applying more chemical fertilizers to their fields; however, while this practice has increased crop yields, it has been devastating for ecology. Agriculture has become one of the biggest polluters of the nation’s precious water supply. Rivers, lakes, and underground reserves of water are being filled in and poisoned by soil and chemicals carried by drainage from eroding fields, Furthermore, fertilizers only replenish the soil; they do not prevent its loss.7. Clearly something else has to be done in order to avoid an eventual ecological disaster. Conservationists insist that the solution to the Problem lies in new and better farming techniques. Concerned farmers are building terraces on hilly fields, rotating their crops, and using new plowing methods to cut soil losses significantly. Substantial progress has been made, but soil erosion is far from being under control.8. The problems and innovations of the agricultural industry in the Midwest are not restricted to growing crops. Livestock raising, which is a big business in the central region of the United States, is also undergoing many changes. Recent developments in technology have enabled farmers to raise not only healthier animals, but more animals as well. By employing the techniques of superovulation, artificial insemination,and embryo transfer, farmers can more than triple the number of offspring produced by a single cow per year.9. The procedure of accomplishing this remarkable feat is as follows. First , the farmer chooses a cow on the basis of certain valuable traits,such as rapid weight gain or high milk production. A veterinarian then injects the cow with hormones which cause the animal to superovulate,that is, to produce more eggs, or“ova”,than the usual one or two. As many as ten or more ova may be released in one superovulation.10. While the ova are moving down the Fallopian tubes toward the uterus，about five days after superovulation, the cow is artificially inseminated with semen from a prize bull. If the insemination is successful,the eggs are fertilized and become living embryos, each of which has the potential to develop into a calf.11. Next comes the process of embryo transfer. After the embryos have developed in the uterus for six to eight days, they are carefully removed and examined for defects. Each healthy embryo is then implanted in the uterus of a different cow, where it continues to develop. Nine months later the surrogate mother gives birth to a healthy calf to which she is not genetically related. 12.The result of the entire procedure is that a farmer can increase the size of a herd of cows at a rate which was previously impossible. Although three to four calves are the average, as many as ten or more may be produced from the embryos of one mother cow. The possible applications of these techniques are overwhelming when one considers that by freezing an embryo until its sister embryo has been born and become sexually mature, it is even possible for a cow to give birth to its identical twin sister!13. As the world’s population continues to increase, farmers will be called upon to produce more and more life-sustaining food. Constant technological advances in soil conservation and livestock production will be required to keep pace with this ever-growing need. One concern, however, is that while this technology is solving old problems, it may be creating new ones in the process. 8. Para. 13 implies that( )
A、A. the process of embryo transfer may cause new problems in the future
B、B. the world’s food needs are increasing
C、C. soil and water conservation is important
D、D. more and more life-sustaining food should be produced
【正确答案】：A
【题目解析】：P59
