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.
6 M* Y/ e' X. X; z8 w8 J. J+ B) q1 n. m 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.
2 G) X4 X5 q9 C+ s, ` 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 O. common
$ h& z5 C/ e. ~0 {2 F# f3 u 答案：
: c* U" b- U* w/ F1 Z I. I 2. B 3. C 4. D 5. O 6. K 7. N 8. F 9. A 10. E |
发表于 2012-8-14 10:30:44
