y eventually reveal their true significance.4 Above the troposphere to a height of about 50 miles is a zone called the stratosphere. The stratosphere is separated from the troposphere by a zone of uniform temperatures called the tropopause. Within the lower portions of the stratosphere is a layer of ozone gases which filter out most of the ultraviolet rays from the sun. The ozone layer varies with air pressure. If this zone were not there, the full blast of the sun’s ultraviolet light would burn our skins, blind our eyes and eventually result in our destruction. Within the stratosphere, the temperature and atmospheric composition are relatively uniform.5 The layer upward of about 50 miles is the most fascinating but the least known of the three strata. It is called the ionosphere because it consists of electrically charges particles called ions, thrown from the sun. The northern lights ( aurora borealis ) originate within this highly charged portion of the atmosphere. Its effect upon weather conditions, if any, is as yet unknown.
参考答案： D 答案解析：
1Paragraph 2 _____.
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
参考答案： F 答案解析：
2Paragraph 1 _____.
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
参考答案： F 答案解析：
3The troposphere is the warmest part of the atmosphere because it _______.
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.
参考答案： D 答案解析：
4The atmosphere consists of _________.
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.
参考答案： A 答案解析：
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.
参考答案： B 答案解析：
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.
参考答案： B 答案解析：
7Paragraph 4 ______.
A.The Definition and The Description of The Ions B.The Definition And The Description o
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