Chemical fertilizers and insecticides____________

Câu hỏi: Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct answer for each of the questions from 35 to 42.
THE "GREEN REVOLUTION"
From 1950 to 1980, the so-called "Green Revolution"swept the world. World food production doubled with the introduction of a new approach to agriculture. It involved the large- scale cultivation of new types of grain (wheat, corn, and rice), and the extensive use of chemicals and farm machinery.
These features were the cause of the early, enormous success of this "revolution". However, the "Green Revolution"methods no longer appear to be successful. Though the population continues to grow, food production has failed to keep up with it.
There are a number of reasons for this. One reason lies in the expense of the new farming methods. The new kinds of grain produce much more than traditional grains, but only under certain conditions. In order to get maximum production, farmers must use large amounts of expensive chemical fertilizers. They also need to use expensive chemical insecticides since the new grains are more easily damaged by insects. Expensive watering systems are also necesary for these grains, especially in drier areas. Many farmers cannot afford to buy all the chemicals and equipment.
Erosion is another reason for the lower grain production. The large- scale farming of a single crop creates the perfect conditions for erosion. In dry areas, especially, the loss of top soil has lowered the productivity of the land. In these areas, also, grain production has been limited by the lack of water. The new types of grain, in fact, require much more water than the grains people used to grow.
Yet another reason for lower production lies in the nature of the chemicals that farmers have used. Though these fertilizers and pesticides raise production levels at first, they must be used in increasing amounts after that. Many farmers cannot afford to buy more, and so production decreases. These chemicals have other effects that are expensive in the long run. They flow into the ground water, causing pollution and health problems. As people learn about these problems, they put pressure on farmers to further limit their use of chemicals.
Finally, the Green Revolution has brought about social and political conflict that has interfered with food production. The problem lies in the cost of the new agricultural methods. Only the larger land owners can afford to make the necessary investments for maximum production of the new grains. With their profits, the large land owners then buy land from the smaller farmers. This way, the large land owners become ever richer and the number of landless poor people increases. Social tensions naturally increase in this situation.
Clearly, it is time to question the methods of the Green Revolution. Governments and farmers need to look at the oveerall picture and long - term effects. They need to find new methods that will better meet the needs of the world's hungry people and will also be less destructive.
Chemical fertilizers and insecticides____________
A. Rarely have any effect on people.
B. Are both expensive and damaging.
C. Can cause large-scale erosion.
D. Are not always necessary with the new types of grain.