托福考试

【分析解答题】Questions 30-39The atmosphere of Venus is quite different from ours. Measurements taken from theEarth show a high concentration of carton dioxide in the atmosphere of Venus. In fact,carbon dioxide makes up 96 percent of Venus* atmosphere; nitrogen makes up almost all the rest. TheEarth’s atmosphere, by comparison, is mainly nitrogen, with a fair amountof oxygen as well.Carbon dioxide makes up less than 0.1 percent of the terrestrial atmosphere,The surface pressure of Venus* atmosphere is 90 limes higher than the pressure ofEarth’s atmosphere, as a result of the large amount of carbon dioxide in the former.ThroughoutEarth’s history, carbon dioxide onEarth has mixed with rain to dissolve10 rocks; the dissolved rock and carbon dioxide eventually flow into the oceans, where they precipitate to fonn new terrestrial rocks, often with the help of life-forms. If this carbondioside were released from theEarth’s rocks, along with ower carton dioxide trapped inseawater, our atmosphere would become as dense and have as high a preasore as that ofVenus. Venus, slightly closer to the Sun thanEarth and thus hotter, had no’oceans in which the carbon dioxide could dissolve or life to help take up the carbon.Also, Venus has probably lost almost all the water it ever ha
D、Since Venus is closerto the Sun than theEarth is, its lower atmosphere was hotter even early on. The resultwas that more water vapor went into its upper atmosphere, where solar ultraviolet raysbroke in up into hydrogen and oxygen. The hydrogen, a light gas, escaped easily; the oxygen has combined with other gasses or with iron on Venus1 surface.Studies from theEarth show that the clouds on Venus are primarily composed of droplets of sulfuric acid, with water droplets mixed in* Sulfuric acid may sound strangeas a cloud constituent, but theEarth too has a significant layer of sulfuric acid dropletsin its stratosphere. However, the water in the lower layers of theEarth’s atmosphere,circulating because of weather, washes the sulfur compounds out of these layers, whereas Venus has sulfur compounds in me lower layers of its atmosphere in addition to those inits clouds. Avoiding to the passage, what happened to oxygen on Venus’
A、Most of it was absorbed into rocks.
B．It was released from water and then combined with other substances.
C．It chemically combined with hydrogen to form atmospheric water,

D、It has been slowly replacing carbon dioxide in Venus’ upper atmosphere,

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