A.contains a layer of ozone gases.  B.about 42 degrees colder than on the ground.  C.21% oxygen by weight.  D.less than 1% of xenon by volume  E.about 75 degrees colder than in Interlaken  F.is warmed by the earth’s heat.  

5Life as we know exists on the earth because the atmosphere _________.

 A.contains a layer of ozone gases.  B.about 42 degrees colder than on the ground.  C.21% oxygen by weight.  D.less than 1% of xenon by volume  E.about 75 degrees colder than in Interlaken  F.is warmed by the earth’s heat.  

6At the top of Jungfrau, which towers 12,000 feet above the town of Interlaken in Switzerland, the temperature is usually _______.

 A.contains a layer of ozone gases.  B.about 42 degrees colder than on the ground.  C.21% oxygen by weight.  D.less than 1% of xenon by volume  E.about 75 degrees colder than in Interlaken  F.is warmed by the earth’s heat.  

7Paragraph 4 ______.

 A.The Definition and The Description of The Ions  B.The Definition And The Description of The Stratosphere  C.The Sun’s Rays  D.Recent Studies of The Upper Atmosphere Versus Past Studies  E.The Definition And The Description of The Troposphere  F.The Composition of The Atmosphere  

8Paragraph 3 _____.

 A.The Definition and The Description of The Ions  B.The Definition And The Description of The Stratosphere  C.The Sun’s Rays  D.Recent Studies of The Upper Atmosphere Versus Past Studies  E.The Definition And The Description of The Troposphere  F.The Composition of The Atmosphere  

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（第31—45题，每题3分，共45分;下面有3篇短文，每篇短文后有5道题。请根据短文内容，为每题确定1个最佳选项。）1、The Volcano Geologists have been studying volcanoes for a long time. Though they have learned a great deal, they still have not discovered the cause of volcanic action. They know that the inside of the earth is very hot, but they are not sure exactly what causes the great heat. Some geologists have thought that the heat is caused by the great pressure of the earth’s outer layers. Or the heat may be left from the time when the earth was formed. During the last sixty years scientists have learned about radium, uranium, thorium and other radioactive elements. These give out heat all the time as they change into other elements. Many scientists now believe that much of the heat inside the earth is produced by radioactive elements.Whatever the cause of the heat may be, we do know that the earth gets hotter the farther down we dig, in deep mines and oil wells the temperature rises about 10F for each 50 feet. At this rate the temperature 40 miles below the earth’s surface would be over 40000F. this is much hotter than necessary to melt rock. However, the pressure of the rock above keeps most materials from melting at their usual melting points. Geologists believe that the rock deep in the earth may be plastic, or puttylike, in other words, the rock yields slowly to pressure but is not liquid. But if some change in the earth’s crust releases the pressure, the rock melts. Then the hot, liquid rock can move up toward the surface.When the melted rock works its way close to earth’s crust, a volcano may be formed. The melted rock often contains steam and other gases under great pressure. If the rock above gives way, the pressure is released. Then the sudden expansion of the gases causes explosions. Th