2011年英语六级考试：阅读提高练习(24)

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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__1__available; it must therefore be kept in a closed container or held by a gravitational field, as in the__2__of a planet's atmosphere. The distinction was a __3__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__4 __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 __5 __They are both forms of matter that have no __6 __structure, and they both flow readily.
　　The fundamental similarity of liquids and gases becomes clearly apparent when the temperature and pressure are __7__somewhat. Suppose a closed container __8__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 __9__to it. The combination of temperature and pressure at which the densities become __10__is called the critical point.
5 E4 h! f# I$ f8 ?6 [8 r" z　　A. added  B. case     C. prominent   D. held
　　E. equal  F. partially G. example    H. previous
　　I. space  J. lifted   K. permanent   L. particularly
　　M. extended N. raised 0. common
4 V  [- k7 y' W; v7 c. E, j
3 ?% m2 }+ P6 B$ u9 }* E　　Key:I. I 2. B 3. C 4. D 5. O 6. K 7. N 8. F 9. A 10. E