首页
登录
职称英语
What is the main topic of the passage? [br] [originaltext] What makes it ra
What is the main topic of the passage? [br] [originaltext] What makes it ra
游客
2023-11-06
11
管理
问题
What is the main topic of the passage? [br]
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 observer, 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 1/2, 500 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://tihaiku.com/zcyy/3162654.html
相关试题推荐
TheDowJonesindustrialsclosedMondayatits______.[br][originaltext]G
TheDowJonesindustrialsclosedMondayatits______.[originaltext]Galvani
Whatisthenewsmainlyabout?[originaltext]TheDemocraticPeople’sRepubli
Whatisthemaintopicofthepassage?[br][originaltext]Whatmakesitra
Whatisthemaintopicofthepassage?[br][originaltext]Whatmakesitra
WhichofthefollowingisNOTtrueof"jeans"?[br][originaltext]Jeansare
WhichofthefollowingisNOTtrueof"jeans"?[br][originaltext]Jeansare
WhichofthefollowingisNOTtrueof"jeans"?[originaltext]Jeansareveryp
AttheuniversityMr.Robinsonspecializedin______.[br][originaltext]W:Ah,
AttheuniversityMr.Robinsonspecializedin______.[br][originaltext]W:Ah,
随机试题
强迫型人格障碍
某医院消化科室的住院病人中,近几天突然发生多名医院感染病例,此现象属于A.医院感
Windows操作系统中资源管理器进程可由( )启动。A.winlogon.
导致"至虚有盛候"的病机主要是A.阴精和阳气衰竭,外邪侵袭 B.脏腑气血虚极,
截至2015年底,中国创业投资各类机构数已达1775家,同比增长14.4%。其中
小海穴在A.内踝尖下方凹陷处 B.当尺骨鹰嘴与肱骨内上髁之间凹陷处 C.肘横
个人征信系统信息来源,主要包括()。 A.客户通过银行办理贷款业务 B.客
(2019年真题)患儿,男,1岁4个月,家长为预防幼儿缺钙,每日给患儿服用维生素
劳务派遣单位在跨地区派遣劳动者时,被派遣劳动者享有的劳动报酬和劳动条件应当按照(
拖拉架梁的施工工序中,在“拼装路基支墩、墩台顶面支墩和桥孔内支墩一钢梁组拼一拼装
最新回复
(
0
)