vbvav"> The difference between a liquid and a gas is obvious 67 the conditions of temperature and pressure 68 found at the surface of the Earth. A liquid can be kept in an open container and fills it to the level of a free surface. A gas forms no free surface but 69 to diffuse through- out the space available. it must- 70 be kept in a. closed container, as in the 71 of a planet s atmosphere. The distinction was a prominent feature of early theories 72 the phases of matter. In the nineteenth century, for example, one theory 73 that a liquid could be "dissolved" in a vapor without losing its identity, and 74 theory held that the two phases are made up of different kinds of molecules (分子). The theories now prevailing 75 a quite different approach by emphasizing 76 liquids and gases have in common. They are both forms of matter that have no permanent structure, 77 they both flow easily. They are fluids. The 78 similarity of liquids and gases becomes clearly apparent when the temperature and pressure are raised somewhat. 79 a closed container partially filled with a liquid is heated. The liquid expands or in other 80 , becomes less dense. some of it evaporates. In 81 , the vapor above the liquid surface becomes denser as the evaporated molecules are added 82 it. The combination of temperature and pressure at. 83 the densities become equal is 84 the critical point. Above the critical point the liquid and the gas can no longer be 85 . there is a single, undifferentiated fluid phase of 86 density. 67. A．in B．on百考试题－全国最大教育类网站(100test.com) C．under D．beyond 68. A．commonly B．quickly C. speedily D broadly 69. A．intends B．tends C．inclines D．contends 70. A．however B. nevertheless C．so D. therefore 71. A．event B case C. interest D．face百考试题论坛 72. A I presenting B．submitting C．describing D．painting 73. A．maintained B．verified C．prescribed D．displayed 74. A．another B．other C one D．else 75. A．apply B．adapt C take D．conduct 76. A why B．what C how D．that 77. A and B．so C．but D．or 78. A comparative B．crucial C insignificant D fundamental 79. A Suppose B．Prove C 3 Mean D Relate 80. A．means B．ways C words D．cases 81. A proportion B contrast C response D reply 82. A to B on C up D in 83. A this B that E C whose D which 84. A known来源：www.100test.com B defined C．called D referred 85. A classified B recognized C categorized D distinguished 86. A．inevitable B consistent C uniform D persistent 【结构剖析】说明文。本文主要介绍了液体和气体的不同点和相似点。首先提到液体和气体的区别在通常情况是很明显的，随后提到当温度和气压升高时二者的相似性就变得十分明显。 点击进入论坛查看答案>.>.