Cleaning up our air may have made us healthier. A new analysis shows that the number of storms falls when pollution rises, and increases when pollution drops. Further tightening of present pollution controls " could reduce aerosols (气溶胶；悬浮颗粒) so quickly that we have record numbers of tropical storms for the next decade or two" , says Nick Dunstone of the Met Office Hadley Centre in Exeter, UK. Earlier studies found no connection between storm numbers and aerosols' ability to cool the surface by scattering light in the open air. But aerosols also increase the brightness and lifetime of low-level marine clouds. When Nick Dunstone of the Met Office Hadley Centre in Exeter, UK, added this effect into his climate models, the simulated clouds cooled the surface more than expected. Historically, this cooling effect has been strongest in the north Atlantic. Cooling the north Atlantic reduces the energy available to power hurricanes. It also shifts rising and falling air currents further south, increasing wind shear in the Atlantic hurricane nursery. This extra wind shear tears nascent storms apart before they can gain strength. In this way, Dunstone says, changes in aerosol emissions appear to drive cyclical variations in north Atlantic tropical storms. These variations have long been attributed to natural variations in ocean circulation. Throughout the 20th century, aerosol emissions increased with industrialization and decreased in economic slumps. Tropical storms were frequent from the 1930s through to the 1950s, but rarer in the better economic times of the 1960s to mid-1990s. Then pollution controls reduced aerosol levels, and Atlantic hurricanes came roaring back, with 19 in 1995, a record 28 in 2005, and 19 in each of the past three years. Dunstone expects the increase to continue for another two decades. After that, global warming may begin to reduce the number of tropical storms, by warming the air and thus reducing the temperature difference between the sea surface and the atmosphere. It is not clear whether aerosols affect the intensity of storms.

单选题 What can we learn from the first two paragraphs?

【正确答案】 A

【答案解析】解析：根据题干，该题应定位到本文的前两段。A选项中inversely proportional意为“成反比”，也就是说风暴数量和污染指数是成反比的，这正是文章的中心思想，在第一段中也有详细表述，所以A选项正确。B选项指出风暴的数量是和气溶胶冷却海洋表面空气的能力相关的。而第二段第一句指出气溶胶通过散射户外光线来冷却海洋表面空气，而早期的研究并未发现风暴的数量和气溶胶的这种能力有关系。所以B选项不对。C选项“气溶胶增加了海洋云的亮度和寿命”，第二段第二句对其进行了描述，但第二句描述的是增加了低位海洋云层的亮度和寿命，所以C选项也不正确。D选项是对第二段第一句的曲解，第二段第一句指出气溶胶通过对户外光线的散射来冷却海洋表面空气，而D选项指出通过聚集户外光线来冷却海洋表面空气。所以D选项也不正确。

单选题 According to the passage, cooling the north Atlantic________.

【正确答案】 B

【答案解析】解析：根据题干可以将该题定位至第三段。第三段指出：北大西洋表面空气的冷却减少了飓风生成所需的能量，并将上升和下降气流进一步南推，增加大西洋飓风带的风切，从而切断刚刚形成的风暴。Dunstone说，通过这种方式，气溶胶排放量的变化似乎促使了北大西洋热带风暴的周期性变化，这些变化一直都被归结为海洋环流的自然变异。A选项指出北大西洋表面空气的冷却为飓风的形成提供了动力，这与第三段中北大西洋表面空气的冷却增大了风切变，而这种额外的风切变切断形成初期的风暴不符，所以不能选。B选项正确。C选项指出北大西洋表面空气的冷却阻止了风切变，这也不正确。D选项认为北大西洋表面空气的冷却降低了污染指数，这并未在文章中得到明确说明，所以也不正确。

单选题 What does the word "nascent" (Para. 3) mean?

【正确答案】 B

【答案解析】解析：回归到第三段第三句，This extra wind shear tears nascent storms apart before they can gain strength。they指的是storms。在风暴变强大前，也就是在风暴还处于形成初期的状态下就将其切断，所以nascent的同义词是B。该题容易误选成D选项small，但该句并没有明确表示风暴的大小，而是说在它形成的初期和力量增强前。

单选题 Which of the following is the factor that influences aerosol emissions?

单选题 Which of the following can be inferred from the passage?

【正确答案】 D

【答案解析】解析：A选项说因为全球变暖，风暴的数量将会增加。文章最后一段第二句指出全球变暖可能开始造成热带风暴数量的减少。所以A选项不正确。B选项说气溶胶是否影响了风暴的数量仍未确定。文章开头就表述了污染指数与风暴数量的关系，也就说明了气溶胶与风暴数量的关系。最后一段的末句说，气溶胶对风暴强度的影响还未确定，不是说对其数量的影响，所以B选项可以排除。根据第二段最后一句的north Atlantic可以排除C选项。D选项可以根据第四段第二句得到验证。