Part Ⅳ CLOZE ［15 MIN.］
　　Decide which of the choices given below would best complete the passage if inserted in the corresponding blanks. Mark the best choice for each blank on your answer sheet.
　　The difference between a liquid and a gas is obvious___( 26 )___the conditions of temperature and pressure commonly found at the sur face of the Earth. A liquid can be kept in an open container and___( 27 )___it to the level of a free surface. A gas forms no free surface but___( 28 )___to diffuse throughout the space available; it must___( 29 )___be kept in a closed container, as___( 30 )___a planet's atmosphere. The distinction was a prominent feature of early theories___( 31 )___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___( 32 )___different kinds o f molecules(分子). The theories now prevailing___( 33 )___a quit e 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 ea sily. They are fluids.
　　The___( 34 )___similarly of liquids and gases becomes clear ly apparent when the temperature and pressure are raised somewhat.___( 35 )___a closed container partially filled with a liquid is heated. The li quid expands or___( 36 )___, becomes less dense; some of it evapor ates.___( 37 )___, the vapor above the liquid surface becomes dense r as the evaporated molecules are added to it. The combination of temperature an d pressure___( 38 )___the densities become equal is___( 39 )___the critical point. Above the critical point the liquid and the gas can no longer be___( 40 )___; there is a single, undifferentiated fluid phase of uniform density.
　　26.A. in B. on C. under D. beyond
　　27.A. fills B. be filled? C. filling D. to fill
　　28.A. intends B. tends? C. inclines D. contends
　　29.A. however B. nevertheless? C. so D. therefore
　　30． A. in the event of B. in the case of C. with a view to D. with reference to
　　31.A. having described B. described C. describing D. to have described
　　32.A. made up of B. consisted of C. constituted of D. made from
　　33.A. apply B. adapt C. take D. conduct
　　34.A. elementary B. crucial? C. rudimentary D. fundamental
　　35.A. Suppose B. To suppose? C. Being supposed D. Supposed
　　36.A. in a word B. in the meantime C. in other words D. in that case
　　37.A. Similarly B. In contrast C. Furthermore D. Instead
　　38.A. on that B. on which? C. at that D. at which
　　39.A. known B. defined? C. called D. referred to
　　40.A. classified B. recognized? C. categorized D. distinguished