The difference between a liquid and a gas is obvious【C1】______the conditions of temperature and pressure commonly found at the surface of the Earth. A liquid can be kept in an open container and【C2】______it to the level of a free surface. A gas forms no free surface but【C3】______to diffuse throughout the space available; it must【C4】______be kept in a closed container, as【C5】______a planet's atmosphere. The distinction was a prominent feature of early theories【C6】______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 held that the two phases are【C7】______different kinds of molecules(分子). The theories now prevailing【C8】______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 flow easily. They are fluids. The【C9】______similarity of liquids and gases becomes clearly apparent when the temperature and pressure are raised somewhat.【C10】______a closed container partially filled with a liquid is heated. The liquid expands, or【C11】______, becomes less dense; some of it evaporates.【C12】______, the vapor above the liquid surface becomes denser as the evaporated molecules are added to it. The combination of temperature and pressure【C13】______the densities become equal is【C14】______the critical point. Above the critical point the liquid and the gas can no longer be【C15】______; there is a single, undifferentiated fluid phase of uniform density."
单选题
【C1】
【正确答案】
C
【答案解析】condition可与in，on，under搭配，但一般不和beyond搭配使用。其中，bein condition指“身体很好”；on condition后常跟that从句，意为“条件是”；be under theconditions of sth．表示“在某种情况(或条件)下”，符合题意。因此，答案为C。
【答案解析】intend和incline一般以人作主语；tend常与to连用，主语可以是人或物，表示“有某种倾向(或趋势)”，如：People under stress tend to express their full range ofpotential．(处于压力下的人容易发挥自己全部的潜力。)contend常与with连用。所以，B项符合题意。