It didn't happen overnight. The problem of polluted air has been festering for centuries. Suddenly the problem of air pollution is becoming critical and is erupting right before our eyes Not only do our eyes burn as they focus through murky air, but when the air clears, we see trees and vegetation dying. We must realize that this destruction can no longer be pinned to some mysterious cause. The one major culprit is air pollution. Today's air pollution is an unfortunate by-product of the growth of civilization. Civilized mall desires goods that require heavy industrialization and mass production. Machines and factories sometimes pollute and taint the air with substances that are dangerous to man and the environment. These substances include radioactive dust, salt spray, herbicide and pesticide aerosols, liquid droplets of acidic matter, gases, and sometimes soil particles. These materials can act alone to irritate objects and forms of life. More dangerously, they join together to act upon the environment. Only lately have we begun recognizing some of their dangerous consequences. Scientists have not yet been able to obtain a complete report on the effects of air pollution on trees. They do know, however, that sulfur dioxide, fluorides, and ozone destroy trees and that individual trees respond differently to the numerous particulate and gaseous pollutants. Sometimes trees growing in a single area under attack by pollutants will show symptoms of injury or will die while their neighbors remain healthy. Scientists believe this difference in response depends on the kind of tree and its genetic makeup. Other factors, such as the tree's stage of growth and nearness to the pollution source, the amount of pollutant, and the length of the pollution attack also play a part. In short, whether or not a tree dies as a result of air pollution depends on a combination of host and environmental factors. For the most part, air pollutants injure trees. To conifers, which have year-round needles, air pollution causes early balding. In this event, trees cannot maintain normal food production levels. Undernourished and weakened, they are open to attack by a host of insects, diseases, and other environmental stresses. Death often follows. Air pollution may also cause hardwoods to lose their leaves. Because their leaves are borne only for a portion of the year and are replaced the following year, air pollution injury to hardwoods may not be so severe.
单选题
The author attributes today's air pollution to______ A. the growth of civilization B. man's carelessness C. environmental imbalance D. some mysterious cause
【正确答案】
A
【答案解析】[解析] 本题问的是作者把空气污染问题归因于什么。根据第三段的“Today's air pollution is an unforinnate by—product ofthe growth of civilization”——当今的空气污染是人类文明发展 过程中的一个不良副产品，由此可知作者认为是文明发展导致了空气污染，因此正确答案为 A。其他选项与题意不符。
单选题
The resistance of some trees to disease can be traced to______ A. protective foliage B. thick bark C. genetic makeup D. tainted air
【正确答案】
C
【答案解析】[解析] 关于树木对疾病的抗病性的内容可以在第四段找到，作者指出在相同的污染条 件下，长在同一地区的不同的树会做出不同的抗病性反应，“Scientists believe this difference in response depends on the kind of tree and its genetic makeup”，科学家认为这种不同的反应取决 于树的种类及其遗传结构。因此正确答案是C。
单选题
Air pollution causes the most damage to ______ A. hardwoods B. conifers C. fruit trees D. fluorides
【正确答案】
B
【答案解析】[解析] 本文最后两段讨论了空气污染对树木的影响。第五段主要陈述了空气污染对 conifers的危害，它们常常会死掉。第六段指出“air pollution injur)，to hardwoods may not be so severe．”意为对阔叶树的伤害并不严重。因此空气污染对针叶树的伤害最大。正确答案为B。 其他两项未被提及。
单选题
The author implies that the greatest source of pollution is ______ A. heavy industry B. chemical processing plants C. urban expansion D. salt spray
【正确答案】
A
【答案解析】[解析] 本题问的是最主要的污染源。原文第三段第二句指出：“Civilized mall desires goods that reqtfire heavy industrialization and mass production…”，文明的商场需要重工业化条 件下产量大的商品，机器和厂房排放各种对人体和环境有害的污染物。由此可知，作者认为 重工业是造成空气污染的主要来源，因此正确答案是A。
单选题
We can conclude that______ A. air pollution is easier to control than water pollution B. the problem of polluted air is a problem overnight C. the impact of air pollution has been known for centuries D. research on the efforts of air pollution is incomplete