提到四级考试中阅读理解，同学们又要吐槽了，它所占比重为百分之三十五，其重要性不言而喻。想要早点为下半年的四六级考试做准备，就来提前练习四级阅读练习题吧。

　　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.

　　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

　　I. I 2. B 3. C 4. D 5. O 6. K 7. N 8. F 9. A 10. E

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