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
Standing on the rim of the Grand Canyon, gazing across this giant would in the earth’s surface, a visitor might assume that the
Standing on the rim of the Grand Canyon, gazing across this giant would in the earth’s surface, a visitor might assume that the
admin
2009-04-23
66
问题
Standing on the rim of the Grand Canyon, gazing across this giant would in the earth’s surface, a visitor might assume that the canyon had been caused by some ancient convulsion. In fact, the events that produced the canyon, far from being sudden and cataclysmic, simply add up to the slow and orderly process of erosion.
Many millions of years ago the Colorado Plateau in the Grand Canyon area contained 10,000 more feet of rock than it does today and was relatively level. The additional material consisted of some 14 layered formations of rock. In the Grand Canyon region these layers were largely worn away over the course of millions of years.
Approximately 65 million years ago the plateau’s flat surface in the Grand Canyon area bulged upward from internal pressure: geologists refer to this bulging action as upwarping; it was followed by a general elevation of the whole Colorado Plateau, a process that is still going on. As the plateau gradually rose, shallow rivers that meandered across it began to run more swiftly and cut more definite courses. One of these rivers located east of the upwarp, was the ancestor of the Colorado. Another river system called the Hualapai, flowing west of the upwarp, extended itself eastward by cutting back into the upwarp; it eventually connected with the ancient Colorado and captured its waters. The new river then began to carve out the 277-mile-long trench that eventually became the Grand Canyon. Geologists estimate that this initial cutting action began no earlier than 10 million years ago.
Since then the canyon forming has been cumulative. To the corrosive force of the river itself have been added other factors. Heat and cold, rain and snow, along with the varying resistance of the rocks, increase the opportunities for erosion. The canyon walls crumble; the river acquires a cutting tool, tons of debris; rainfall running off the high plateau creates feeder streams that carve side canyons. Pushing slowly backward into the plateau, the side canyons expose new rocks, and the pattern of erosion continues.
选项
A、Patterns of erosion in different mountain ranges.
B、Forces that made the Grand Canyon.
C、The increasing pollution of the Colorado River.
D、The sudden appearance of the Grand Canyon.
答案
B
解析
转载请注明原文地址:https://kaotiyun.com/show/kcR7777K
0
大学英语四级
相关试题推荐
在采用直接标价的前提下,如果需要比原来更少的本币就能兑换一定数量的外国货币,这表明()。
沪深300指数期货合约的合约月份为()。
A、Theyarethemainfactorsinfluencingteensuicide.B、Theyarebeingunfairlycriticized.C、Kidsshouldbeforbiddentouseth
A、Theycanlearntheirfuturemajorinanotherlanguage.B、Theycancommunicatewiththeirclassmatesfreely.C、Theycansucceed
A、Relatingthehealthriskassessmenttohealthcoverage.B、Providingapremiumdiscounttoaninsuredcompany.C、Askingemploye
A、Theyareindulgedinthevirtualworld.B、Theyspendlittletimeontheirschoolwork.C、TheytakeadvantageoftheInternetto
F根据语法结构,宾语从句引导词that前缺少谓语动词。而且根据空格前的完成时标志词has得知此处需填过去分词。空格后的宾语从句theeuroisonlyasstrongasitsweakestlink“欧元最强的一面也是其最弱的一面”是一
A、Becauseantibioticshavestrongsideeffects.B、Becauseantibioticsdon’ttargetvirusescausingacold.C、Becauseantibiotics
A、Three.B、Five.C、Seven.D、Nine.CHowmanycoloredlightsmakeupthesunlight?
A、Tuesday.B、Wednesday.C、Thursday.D、Friday.C[听力原文]M:HasthelatestShanghaiDailyarrivedyet?TodayisalreadyTuesday.W:
随机试题
二级反应2A→B,当A的初始浓度为0.200mol/L时半衰期为40s,则该反应的速率常数是()。
A.轻度皮肤黏膜出血伴骨髓增生低下,雄激素治疗有效B.血小板数量减少伴巨核细胞成熟障碍C.红系增生活跃,骨髓细胞外铁消失D.维生素B12、叶酸测定下降,骨穿示巨幼性改变E.严重内脏出血伴三系血细胞下降,骨髓多部位增生极度低下,无巨幼细胞见于巨幼
根据高血压的诊断标准,成人的正常血压是
腰椎间盘突出多发生于
八脉交会穴中通于阳维脉的腧穴是()
盘盈的固定资产应该通过()科目核算。
公安科研主要是围绕有关公安工作的社会现象进行的研究工作。()
市场上存在羽绒服夏天便宜冬天贵,南方便宜北方贵的现象,造成这种价格变动的主要原因是()。
凡是开庭审理的案件,都应当公开审理。()
有三个关系R、S和T如下:则由关系R和S得到关系T的操作是
最新回复
(
0
)