Reading Comprehension
Directions: Read the following passage. Choose the best answer from the four choices marked A, B, C and D for each question. 

     Farmers in the 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 demand of a hungry world.
     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% of the amount sold in world market.
     This productivity, however, has its price. Intensive cultivation exposes the earth to the damaging forces 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.
     Each field is covered by a limited amount of topsoil, the upper layer of earth which is the richest in the nutrient and minerals necessary 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 topsoil 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% over the next 50 years.
     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 on 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 the drainage from eroding fields. Furthermore, fertilizers only replenish the soil; they do not prevent its loss.
     Clearly something else has to be done in order to avoid an eventual ecological disaster. Conservationists insist that the solution to this 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 loss significantly. Substantial progress has been made, but soil erosion is far from being under control.