41)__________. The mystery involves a change in the atmoshpere—a hole, or thinning, of the ozone in the atmosphere over Antarctica. Scientists were not sure what was causing it.
42) __________. It is found both in the air we breathe and in the upper atmosphere. Near the earth, ozone in the air is a danger to life. It is a pollutant. But ozone found 10 kilometers to 50 kilometers up in the atmosphere protects life on earth. Ozone forms in the atmosphere through the action of solar radiation. Once formed, the ozone blocks harmful radiation from reaching the earth. Scientists say a decrease in ozone and an increase in the harmful radiation will cause many more cases of skin cancer and will harm crops, animals and fish.
43) __________.
Chlorine is released into the air from the chlorofluorocarbons—or CFCs—used in plastic, air conditioners and spray cans. The use of CFCs has greatly increased worldwide since 1960 and is continuing to increase.
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{{B}}One Good Reason to Let Smallpox
Live{{/B}} It’s now a fair bet that we will never see the total extinction of the smallpox virus. The idea was to cap the glorious achievement of 1980, when smallpox was eradicated in the wild, by destroying the killer virus in the last two labs that are supposed to have it — one in the US and one in Russia. If smallpox had truly gone from the planet, what point Was there in keeping these reserves {{U}} (1) {{/U}}reality, of course, it was naive to{{U}} (2) {{/U}}that everyone would let{{U}} (3) {{/U}}of such a potent potential weapon. Undoubtedly several nations still have{{U}} (4) {{/U}}vials.{{U}} (5) {{/U}}the last "official" stocks of live virus bred mistrust of the US and Russia,{{U}} (6) {{/U}}no obvious gain. Now American researchers have{{U}} (7 A. keep B. put C. destroy D. eradicate [判断题]危害点指可能发生事故，并能造成人员重大伤亡、设备系统造成重大损失的生产现场。
A.正确 B.错误 [简答题]直线轨距标准为<--NRC-->mm。
[判断题]用户申请改压,由改压引起的工程费用由供电企业和用户各负担50%。
[1分] A.正确 B.错误 我来回答: 提交
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