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  3. 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

admin2016-04-30  80
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).
We can learn from the first paragraph that _____.
选项 A、there are no volcanic activities on hot spots
B、most hot spots are located in the inner part of a plate
C、hot spots usually lie at the boundaries of drifting plates
D、the passage of plates through hot spots will leave dead volcanoes
答案B
解析 根据题干直接查找到第1段。第2句第2个分句提到“其中很多位于板块内部的深处”，而表达同样含义的是B选项。该段第1句指出，这些互不相连、发生火山运动的小地区，地质学家称之为热点，可见A项错误。选项C与第2句第1个分句的内容相反。倒数第2句提到“在某些情形下，板块移动经过热点留下死火山的痕迹”，即不是所有板块移动都会留下死火山的痕迹，故D错。
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