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
What is the main topic of the passage?
What is the main topic of the passage?
admin
2010-04-24
47
问题
What is the main topic of the passage?
What makes it rain? Rain falls from clouds for the same reason anything falls to Earth. The Earth’s gravity pulls it. But every cloud is made of water droplets or ice crystals. Why doesn’t rain or snow fall constantly from all clouds? The droplets or ice crystals in clouds are exceedingly small. The effect of gravity on them is minute. Air currents move and lift droplets so that the net downward displacement is zero, even though the droplets are in constant motion.
Droplets and ice crystals behave somewhat like dust in the air made visible in a shaft of sunlight. To the casual ob-server, dust seems to act in a totally random fashion, moving about chaotically without fixed direction. But in fact dust particles are much larger than water droplets and they finally fall. The cloud droplet of average size is only 1/2500 inch in diameter. It is so small that it would take sixteen hours to fall a mile in perfectly still air, and it does not fall out of moving air at all. Only when the droplet grows to a diameter of 1/125 inch or larger can it fall from the cloud. The average raindrop contains a million times as much water as a tiny cloud droplet. The growth of a cloud droplet to a size large enough to fall out is the cause of rain and other forms of precipitation. This important growth process is called "coalescence"
选项
A、They are balanced by the pressure of rain droplets.
B、The effect of gravity at high altitude is random.
C、They are kept in the sky by air current.
D、They are moving about with fixed direction.
答案
C
解析
转载请注明原文地址:https://kaotiyun.com/show/8s2K777K
0
专业英语四级
相关试题推荐
Theagreementcomesonthefirstdayofrenewedpeacetalksbetweenallsidesinthe_________civilwar.
Whatarethespeakersprobablygoingtodo?
Whatarethespeakersprobablygoingtodo?
Whatarethespeakersprobablygoingtodo?
Betweengettingupandhermeeting,thewomanhadabout______.
What’sthechangeinAmericanfamilyinthe21century?
WhatwillbetheKosovosituationinthenearfuture?
Doeschildhoodhaveahistory?AttheturnoftheeighteenthandnineteenthcenturiesWilliamWorthworthwroteofchildhoodand
Jackisso______tohisappearancethatheneverhashisclothespressed.
随机试题
简述肌力分级。
男性43岁,血压高一周。血压160/98mmHg,体重70kg,BMI25.6,血尿常规、肝肾功能、血糖,甘油三酯、胆固醇、眼底、超声心动图检查均正常。患者不嗜烟酒,家族史(一)。目前应采用的处理
胃热者的口气多
侵权与违约竞合的期货纠纷案件,依()确定管辖。
下列关于税制要素的表述正确的是()。
资料一思达公司前身是C国J省一家冷气设备生产企业。1985年开始,公司集中资源研发、生产当时国内市场处于一片空白的家用空调和大型柜式空调,企业获得了迅猛发展。到1994年,思达公司已成为C国最大空调生产基地。1994年,思达公司积累了大量的
定义:(1)感觉是人们的感官对多种不同能量的觉察,并转换成神经冲动。(2)知识就是对客体的如实区别或联系。(3)推理是运用一定的法则从已有知识得出新知识的思维活动。典型例证:(1)竹竿浸入水中被水折成两段,出水后竹
简述物权法的基本原则。
A.对不起,我正忙呢,你问别人吧!B.我已经准备好了,在左边的包里。C.冬天到了,天气越来越冷。D.这几天经常刮风,不方便出门。现在我每天早上打扫房间,也是一种运动。E.没了,我正在洗呢!你最近还是每天早上去公园锻炼吗?()
A、Hewillpostponethetrip.B、Hewilltaketennislessons.C、Hewillmarrythewoman.D、Hewillcookdinnerforthewoman.B选项均
最新回复
(
0
)