E Ways to Reduce Soot Emission
F Greenhouse Gases as the Main Factor of Global Warming
5. In the twentieth century， soot_________ 。
6. Hansen cautioned that greenhouse gases_________ 。
7. Black soot covered snow and ice_________ 。
8. A soot forcing is unusually effective， which_________ 。
A produces much more global warming than a carbon-dioxide forcing of the same magnitude
B contributed to 25 percent of observed global warming
C can produce greenhouse gases
D absorb more of suns energy and warmth than white background
E still surpass soot in warming the worlds climate during the last century
F can be seen mostly in the Northern Hemisphere
「正确答案」
1-4 CAFB
5-8 BEDA
「答案解析」
1.C 第三段解释了为什么soot会增加地球升温效应。
2.A 第四段介绍了soot在两方面起的作用：(1)soot增加了雪吸收太阳能量和热量的能力；(2)soot导致海洋和陆地上空的大气层发生变化。
3.F 第六段的关键句子是：“……greenhouse gases are the primary cause of climate warming during the past century.”
4.B 第七段介绍了在研究北半球的纬度、雪覆盖面和日照诸因素与气温升高之间的关系方面取得的成果。
5.B 选择B的依据是第一段。有关的句子是：“……black soot may be responsible for 25 percent of observed global warming over the past century.”选项B中用了过去式contributed，也是选B的一个线索，因为第五题的题干中有in the twentieth century，这个时间状语要求谓语动词用过去式，而4个选项中只有B项的动词用的是过去式。
6.E Hansen cautioned和greenhouse gases仅出现在第六段。该段的大意是：虽然煤烟在改变全球气候方面所起的作用相当显著，但是上个世纪气温上升的主要因素还是温室气体。选项E概括了第六段的意思。
7.D 本题答案的依据是第二段第一句。
8.A 本题答案的依据是第五段的下列句子： Soots increased absorption of solar energy is especially effective in warming the worlds climate.“This forcing is unusually effective， causing twice as much global warming as a carbon-dioxide forcing of the same magnitude，”Harisen noted.
