单选题 There are hidden factors which scientists call "feedback mechanisms". No one knows how they will interact with the changing climate. Here"s one example: plants and animals adapt to climate change over centuries. At the current estimate of half a degree centigrade of warming per decade, vegetation (植物) may not keep up. Climatologist James Hansen predicts climate zones will shift toward the poles by 50 to 75 kilometres a year—faster than trees can naturally migrate. Species that find themselves in an unfamiliar environment will die. The 1,000-kilometre-wide strip of forest running through Canada, the USSR and Scandinavia could be cut by half. Millions of dying trees would soon lead to massive forest fires, releasing tons of CO ₂ and further boosting global warming.
There are dozens of other possible "feedback mechanisms". Higher temperatures will fuel condensation and increase cloudiness, which may actually damp down global warming. Others, like the "albedo" effect, will do the opposite. The "albedo" effect is the amount of solar energy reflected by the earth"s surface. As the northern ice and snow melt and the darker sea and land pokes (戳) through, more heat will be absorbed, adding to the global temperature increase.
Even if we were to magically stop all greenhouse-gas emissions tomorrow, the impact on global climate would continue for decades. Delay will simply make the problem worse. The fact is that some of us are doing quite well the way things are. In the developed world prosperity has been built on 150 years of cheap fossil fuels.
Material progress has been linked to energy consumption. Today 75 percent of all the world"s energy is consumed by a quarter of the world"s population. The average rich world resident adds about 3.2 tons of CO2 yearly to the atmosphere, more than four times the level added by each Third World citizen. The U.S., with just seven percent of the global population, is responsible for 22 percent of global warming.

单选题 "Feedback mechanisms" in Paragraph 1 most probably refers to ______.

【正确答案】 B

【答案解析】[解析] 该题的答案见第一段的首句，科学家把“一些不明因素”称之为feedback mechanisms，然后接着说：No one knows how they will interact with the changing climate. Here"s one example: plants and animals adapt to climate change over centuries.(没人知道它们是如何与气候变化相互作用的。)故选项B正确。

单选题 James Hansen predicts that the shift of climate zones will be accompanied by ______.

【正确答案】 D

【答案解析】[解析] 该题的答案见第一段的中间部分，根据气象专家James Hansen的预测，气候带每年将向两极移动的速度为50～75千米，faster than trees can naturally migrate. Species that find themselves in an unfamiliar environment will die.(快于树木自然迁移的速度。物种在自己不熟悉的环境中将会死亡。)可见成千上万的树木的死亡原因在于跟不上这一速度，适应不了这种新环境而死亡。故选项D正确。

单选题 We can learn from the passage that ______.

【正确答案】 A

【答案解析】[解析] 该题的答案见第二段的起首两句：There are dozens of other possible "feedback mechanisms". Higher temperatures will fuel condensation and increase cloudiness, which may actually damp down global warming.(还有其他许多可能的“反馈机制”。高温将促使云层凝结和增厚，可能减缓全球气候变暖。)其中的damp down与选项A中的slow down同义，故选项A正确。

单选题 It can be inferred from the passage that ______.

【正确答案】 B

【答案解析】[解析] 该题的答案见第四段的第三句：The average rich world resident adds about 3.2 tons of CO ₂ yearly to the atmosphere, more than four times the level added by each Third World citizen(富裕国家的居民每年人均向大气层释放3.2吨的二氧化碳，是第三世界居民人均水平的4倍多。)这也就是说第三世界国家的公民每年向大气层释放的CO ₂ 还不到1吨，故选项B正确。