2. 外语
  3. A. solid B. made up of C. equal D. fills E. describing F. vapor G. therefore H. fundamental I. elementary J. distinguished

A. solid B. made up of C. equal D. fills E. describing F. vapor G. therefore H. fundamental I. elementary J. distinguished

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问题     A. solid B. made up of C. equal D. fills E. describing
    F. vapor G. therefore H. fundamental I. elementary J. distinguished
    K. flow L. refuting M. consisted of N. however O. dense
    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 【C1】______ it to the level of a free surface. A gas forms no free surface but tends to diffuse throughout the space available; it must【C2】______ be kept in a closed container, as in the case of a planet’s atmosphere. The distinction was a prominent feature of early theories【C3】______ the phases of matter. In the nineteenth century, for example, one theory maintained that a liquid could be "dissolved" in a【C4】______ without losing its identity, and another theory held that the two phases are【C5】______ different kinds of molecules. The theories now prevailing take a quite different approach by emphasizing what liquids and gases have in common. They are both forms of matter that have no permanent structure, and they both【C6】______ easily. They are fluids.
    The【C7】______similarity of liquids and gases becomes clearly apparent when the temperature and pressure are raised somewhat. Suppose a closed container partially filled with a liquid is heated.
    The liquid expands, or in other words, becomes less【C8】______; some of it evaporates. In contrast, the vapor above the liquid surface becomes denser as the evaporated molecules are added to it. The combination of temperature and pressure at which the densities become【C9】______ is called the critical point. Above the critical point the liquid and the gas can no longer be【C10】______ ; there is a single, undifferentiated fluid phase of uniform density.
【C2】
选项
答案G
解析 空格所在分句成分完整，因此推测空格处填入副词。前面一句说到气体会在空气中扩散，此处说要装在密封的容器里，前后分句逻辑上存在“因果”关系，备选副词中的therefore“因此”符合要求，故选G。however表示“转折”关系，不符合此处的逻辑关系，故可排除。
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