大学英语四六级考试阅读提高的练习（22）

　　11 available; it must therefore be kept in a closed container or held by a gravitational field, as in the 12 of a planets 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 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

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