首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
It didn’t happen overnight. The problem of polluted air has been festering for centuries. Suddenly the problem of air pollut
It didn’t happen overnight. The problem of polluted air has been festering for centuries. Suddenly the problem of air pollut
admin
2012-07-18
62
问题
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 envimnmental 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 partion of the year and are replaced the following year.air pollution injury to hardwoods may not be so severe.
We can conclude that____.
选项
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
答案
D
解析
题目问:通过文章内容我们可以得出什么结论?第四段第一句“Scientists have not yet been able to obtain a complete report on the effects of air pollution on trees.”通过这句话可知,关于空气污染对树木的影响问题,科学家还没有得到完整的结论。据此判断,应选择D。
转载请注明原文地址:https://kaotiyun.com/show/b4nO777K
0
考博英语
相关试题推荐
Sheremainsconfidentand______untroubledbyourpresentproblems.
AttheKyotoconferenceonglobalwarminginDecember1997,itbecameabundantlyclearhowcomplexithasbecometoworkoutint
AttheKyotoconferenceonglobalwarminginDecember1997,itbecameabundantlyclearhowcomplexithasbecometoworkoutint
Mosttechnicalprofessionalswanttoworkonproblemsthatarecriticaltothesuccessofthefirm.Theywanttoknowwhatthef
WhenyouwatchafootballgameonaSaturdayafternoon,youfeelsecureinyourknowledgeofwhatwillhappenwhenaplayerboot
OneofNike’sfounders,PhillipHampsonKnighthadbeenatopathletewhenhewasattheUniversityofOregonandhemovedonto
Mostpeoplewhotravellongdistancescomplainofjetlag.Jetlagmakesbusinesstravelerslessproductiveandmoreprone【51】maki
Mostpeoplewhotravellongdistancescomplainofjetlag.Jetlagmakesbusinesstravelerslessproductiveandmoreprone【51】maki
Mostpeoplewhotravellongdistancescomplainofjetlag.Jetlagmakesbusinesstravelerslessproductiveandmoreprone【51】maki
Itisironicthatthe______insightsofthegreatthinkersarevoicedsooftenthattheyhavebecomemere
随机试题
原发综合征
治疗肺阴亏损肺痨,宜选用治疗肺阴亏损虚劳,宜选用
深感觉包括()
天线应该在避雷针()保护范围内。
秘书应掌握的手工文字记录方法有()。
我国的国家结构形式属于()。
对城市建设焕然一新的追求,不仅会使城市记忆受到损坏甚至毁灭,也是对城市中人的生活情感的______。城市中长期积淀形成的文化风格和人文环境,被当作了“过时”的东西予以______或抛弃,城市记忆也因此没有了依托对象,公众的情感认同无法被唤起,在心灵上就会出
[2007年]设三阶实对称矩阵A的特征值λ1=1,λ2=2,λ3=-2,α1=[1,-1,1]T是A的属于λ1的一个特征向量.记B=A5-4A3+E,其中E为三阶单位矩阵.验证α1是矩阵B的特征向量,并求B的全部特征值与特征向量;
设n阶方程A=(α1,α2,…,αn),B=(β1,β2,…,βn),AB=(γ1,γ2,…γn),记向量组(I):1,α2,…,αn,(Ⅱ):β1,β2,…,βn,(Ⅲ):γ1,γ2,…γn,如果向量组(Ⅲ)线性相关,则().
Windows98中,可以打开“开始”菜单的组合键是()。
最新回复
(
0
)