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.
【C4】
选项
答案F
解析 空格前的a提示空格处应填入可数名词单数。此处主要讲的是“液体”和“气体”是物质的不同阶段，空格前已经提到“液体”，因此推断此处应填入表示“气体”的词，词库中的vapor“蒸汽”符合要求。原文并未提到“固体”，因此排除solid“固体”。
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