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
Scattered around the globe are more than 100 small regions of isolated volcanic activity known to geologists as hot spots. Unlik
Scattered around the globe are more than 100 small regions of isolated volcanic activity known to geologists as hot spots. Unlik
admin
2019-06-23
58
问题
Scattered around the globe are more than 100 small regions of isolated volcanic activity known to geologists as hot spots. Unlike most of the world’s volcanoes, they are not always found at the boundaries of the great drifting plates that make up the earth’s surface; on the contrary, many of them lie deep in the interior of a plate. Most of the hot spots move only slowly, and in some cases the movement of the plates past them has left trails of dead volcanoes. The hot spots and their volcanic trails are milestones that mark the passage of the plates.
That the plates are moving is now beyond dispute. Africa and South America, for example, are moving away from each other as new material is injected into the sea floor between them. The complementary coastlines and certain geological features that seem to span the ocean are reminders of where the two continents were once joined. The relative motion of the plates carrying these continents has been constructed in detail, but the motion of one plate with respect to another cannot readily be translated into motion with respect to the earth’s interior. It is not possible to determine whether both continents are moving in opposite directions or whether one continent is stationary and the other is drifting away from it. Hot spots, anchored in the deeper layers of the earth, provide the measuring instruments needed to resolve the question. From an analysis of the hot-spot population it appears that the African plate is stationary and that it has not moved during the past 30 million years.
The significance of hot spots is not confined to their role as a frame of reference. It now appears that they also have an important influence on the geophysical processes that propel the plates across the globe. When a continental plate comes to rest over a hot spot, the material rising from deeper layer creates a broad dome. As the dome grows, it develops deep fissures(cracks); in at least a few cases the continent may break entirely along some of these fissures, so that the hot spot initiates the formation of a new ocean. Thus just as earlier theories have explained the mobility of the continents, so hot spots may explain their mutability(inconstancy).
That Africa and South America were once joined can be deduced from the fact that _____.
选项
A、the two continents are still moving in opposite directions
B、they have been found to share certain geological features
C、the African plate has been stable for 30 million years
D、over 100 hot spots are scattered all around the globe
答案
B
解析
从第2段的第3句可知,非洲和南美洲曾经连接在一起的证据有两个——海岸线所具有的互补的特征(complementary coastlines)及某些地质特点(certain geological features)。B项符合后者,故为正确答案。
转载请注明原文地址:https://kaotiyun.com/show/9JX7777K
0
大学英语六级
相关试题推荐
科举制度(theimperialexamination)是中国帝制时期(imperialChina)选拔官员的制度,具有1300多年的历史。它将阅读、考试和选拔政府官员三者紧密结合起来,是一种公平和公开的人才选举方法,是中国选举史上的一大突破。它为中
PresidentBarackObama’spicktoheadtheEnvironmentalProtectionAgency(EPA),LisaJackson,hasspent20yearsasanenvironm
A、Stayinginaglassboxfor44daysjustwithwater.B、ThrowingcheeseburgersonaplanearoundLondon.C、Havinghisresearchp
A、Studentslearnbestbydoingthingsforreal.B、Studentslearnfastinbusinessenvironment.C、Studentslearnfastthroughonl
A、Thelevelofeducationvariesaroundtheworld.B、Theeconomists’attitudestopopulationdiffergreatly.C、Thelivingstandar
A、StudentsfromAmericaB、StudentsfromEngland.C、StudentsfromAustraliaD、StudentsfromJapan.A
A、Studyinginaforeignenvironment.B、Livingfarawayfromfamily.C、Returningbacktohomecountry.D、Fittingintoaforeignc
A、Mealsareprovidedfreeofcharge.B、Studentsaremoresecure.C、Studentsneedn’tdevotetimetohousekeeping.D、Studentshave
A、Above50%.B、About25%.C、Around68%.D、Approximately94%.B
随机试题
尘肺的X线改变中,不规则小阴影的病理基础为
在工程建设参与方中,()已成为项目业主不可或缺的助手,承担着本来由业主实施的管理工作。
场地自然坡度为16%时,应选()设计场地连接形式。
()都是消防工作的主体,共同构筑消防安全工作格局,任何一方都非常重要,不可偏废。
对单一客户进行授信限额管理时,商业银行对客户进行信用评级后,首要工作是要确定该客户的()
某债券面值100元,每年按5元付息,10年还本,则其名义收益率是()。
保险公司应当及时将核定结果通知旅行社以及受害人;对属于保险责任的,在与旅行社达成赔偿保险金的协议后()内,履行赔偿保险金义务。
1~3岁儿童心理发展有哪些特征?
设向量α=[a1,a2,…,an]T,β=[b1,b2,…,bn]T都是非零向量,且满足条件αTβ=0,记n阶矩阵A=αβT,求:A能否相似于对角矩阵,说明理由.
证明若f(x)为奇函数,且f′(x0)=A,则f′(一x0)=A.
最新回复
(
0
)