B Observations of Warming in the Northern Hemisphere
4．Paragraph 7 __．
The researchers found that observed warming in the Northern Hemisphere was large in the winter and spring at middle and high latitudes．（These observations were consistent with the researchers’climate model simulations, which showed some of the 1argest warming effects occurred when there were heavy snow cover and sufficient sunlight．）
4． B．分析：段首句中出现了Northern Hemisphere，而接下来的句子中出现了“These observations”，这些词都被包含在B中，因此判断B是答案。
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 sun’s energy and warmth than white background
E ．still surpass soot in warming the world’s climate during the last century
F ．can be seen mostly in the Northern Hemisphere
5． In the twentieth century, soot ___．
5． B．分析：结合文章标题（主题）Soot （煤灰） and Snow：a Hot Combination，判断B很可能是答案。也可以借助文章中的相关语句：According to a computer simulation，black soot may be responsible for 25 percent of observed global warming over the past century．
A． produces much more global warming than a carbon-dioxide forcing of the same magnitude
C． can produce greenhouse gases
D． absorb more of sun’s energy and warmth than white background
E． still surpass soot in warming the world’s climate during the last century
F． can be seen mostly in the Northern Hemisphere
6．Hansen cautioned that greenhouse gases__．
6．E． 分析：文章中提到温室气体仍然是造成全球温度上升的主要因素，因此判断E是答案。
A． produces much more global warming than a carbon-dioxide forcing of the same magnitude
C． can produce greenhouse gases
D． absorb more of sun’s energy and warmth than white background
F ．can be seen mostly in the Northern Hemisphere
7． Black soot covered snow and ice__．
7． D．分析：该题可以借助常识直接判断D是答案（带有煤灰的冰和雪要比白色的背景吸收的热量多）。
A． produces much more global warming than a carbon-dioxide forcing of the same magnitude
C． can produce greenhouse gases
F． can be seen mostly in the Northern Hemisphere
8． A soot forcing is unusually effective，which__．
8． A．分析：借助提干中的核心词soot forcing作为答案线索，这样发现答案相关句：Soot’s increased absorption of solar energy is especially effective in warming the world’s climate．“This forcing is unusually effective，causing twice as much global warming as a carbon-dioxide forcing of the same magnitude（数量）．
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