17年英语专四完形填空训练

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The difference between a liquid and a gas is obvious under the conditions of temperature and pressure commonly found at the surface of the Earth. A liquid can be kept in an open container and fill it to the level of a free surface. A gas forms no free surface but tends to diffuse throughout the __11__ available; it must therefore be kept in a closed container or held by a gravitational field, as in the __12__ of a planet's atmosphere. The distinction was a __13__ feature of early theories describing the phases of matter. In the nineteenth century, for example, one theory maintained that a liquid could be "dissolved" in a vapor without losing its identity, and another theory __14__ that the two phases are made up of different kinds of molecules. The theories now prevailing take a quite different approach by emphasizing what liquids and gases have in__15__They are both forms of matter that have no__16__ structure, and they both flow readily.

The fundamental similarity of liquids and gases becomes clearly apparent when the temperature and pressure are __17__somewhat. Suppose a closed container__18__ filled with a liquid is heated. The liquid expands, or in other words becomes less dense; some of it evaporates. In contrast, the vapor above the liquid surface becomes denser as the evaporated molecules are__19__ to it. The combination of temperature and pressure at which the densities become __20__is called the critical point.

A. added B. case inent

E. equal F. partially ple ious

I. space ed anent icularly

M. extended N. raised on

　　参考答案

II. I 12. B 13. C 14. D 15. O 16. K 17. N 18. F 19. A 20. E

During the nineteenth and twentieth centuries, migrations have taken place within 11 countries; the cities with their industries have attracted people away from the country. The possibility of earning a fixed 12 in a factory or office was more attractive than the possibility of staying on the farm and having one's work 13 by frost, storms, or droughts. Furthermore, the

development of agricultural machinery made it possible for fewer people to do the same 14 of work.

Thus, at the same time when the industrial revolution made it possible to produce goods more 15 and more quickly in factories, agricultural revolution also took place. Instead of leaving fields empty every third year, farmers began to plant clover or some other crop that would 16 the soil. Instead of using only animal fertilizer, farmers began to use chemical fertilizers to keep the soil

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rich. These methods have enabled French farmers, for example, to get five times as much wheat as was 17 from the same land two centuries ago.

In many countries farmers find it more 18 to raise only one crop or one kind of animal. They choose the kind that gives the best results. Then they sell all that they produce, instead of trying to grow a little of everything and consume what they grow. This is a more feasible type of 19 because modern methods and machinery are adapted to specific animals and specific crops. Therefore, it would be too expensive to do all the work by hand, or to buy the 20 needed for several different kinds of farming.

A. salary E. deserted I. equivalent M. destroyed

B. freely F. operation J. enrich N. certain

C. profitable nt K. fruitful O. cheaply

D. obtained H. payment L. equipment

　　参考答案

II. N 12. A 13. M 14. G 15. O 16. J 17. D 18. C 19. F 20. L