阅读题：A growing world population and the discoveries of science may alter this pattern of distribution in the future

Questions 31 to 35 are based on the following passage.

A growing world population and the discoveries of science may alter this pattern of distribution in the future. As men slowly learn to master diseases, control floods, prevent famines, and stop wars, fewer people die every year; and in consequence the population of the world is steadily increasing. In 1925 there were about 2,000 million people in the world; by the end of the century there may well be over 4,000 million.

When numbers rise the extra mouths must be fed. New lands must be brought under cultivation, or land already farmed made to yield larger crops. In some areas the accessible land is so intensively cultivated that it will be difficult to make it provide more food. In some areas the population is so dense that the land is parceled out in units too tiny to allow for much improvement in farming methods. Were a large part of this farming population drawn off into industrial occupations, the land might be farmed much more productively by modern methods.

There is now a race for science, technology, and industry to keep the output of food rising faster than the number of people to be fed. New strains of crops are being developed which will thrive in unfavorable climates: there are now farms beyond the Arctic Circle in Siberia and North America; irrigation and dry-farming methods bring arid lands under the plough, dams hold back the waters of great rivers to ensure water for the fields in all seasons and to provide electric power for new industries; industrial chemistry provides fertilizers to suit particular soils; aeroplanes spray crops to destroy locusts and many plant diseases. Every year some new means is devised to increase or to protect the food of the world.

31. The author says that the world population is growing because _____.

A) there are many rich valleys and fertile plains

B) the pattern of distribution is being altered

C) people are living longer

D) new land is being brought under cultivation

32. The author says that in densely populated areas the land might be more productively farmed if _____.

A) the plots were subdivided

B) a large part of the people moved to a different part of the country

C) industrial methods were used in farming

D) the units of land were made much larger

33. We are told that there are now farms beyond the Arctic Circle. This has been made possible by _____.

A) producing new strains of crops

B) irrigation and dry-farming methods

C) providing fertilizers

D) destroying pests and disease

34. Which of these words is nearest in meaning to the word "strains"？

A) types B) sizes

C) seeds D) harvests

35. The author's main purpose is to _____.

A) argue for a belief B) describe a phenomenon

C) entertain D) propose a conclusion