单选题 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 not beyond dispute. Africa and South America, for example, are moving away from eath 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 come to rest over a hot spot, the material rising from deeper layer creates a broad dome. As the dome grows, it develops seed 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 (inconstant).
单选题 The author believes that ______.
【正确答案】 B
【答案解析】[解析] 从文章第1段的内容可知，地球上散布着一百多个热点；大部分热点区移动极其缓慢，某些情况下，板块滑过这些热点区，便留下死火山的痕迹；热点区及其火山痕迹是板块移动的象征。从文章第2段的内容可知，如今，板块漂移学说已是无需质疑的了；然后举例进一步说明。从文章最后一段的内容可知，热点的重要性并不仅限于作为参照体系这一作用上；现在看来，它们对推动板块在地球上移动的地球物理学的过程也产生了重大影响；因此，正如早期的理论解释了大陆的移动那样，热点或许可以解释大陆的易变性。据此可知，作者认为有关大陆移动的理论是正确的。B项与文章的意思相符，因此B项为正确答案。
单选题 That Africa and South America were once joined can be deduced from the fact that ______.
【正确答案】 B
【答案解析】[解析] 本题可参照文章的第2段。从中可知，因为有新物质深入洋底，两个大陆距离愈来愈远；互补的海岸线以及似乎横跨海洋的地质地貌特征提示人们——这两块大陆曾经连接在一起；人们既不能确定是否这两块大陆在向相反的方向移动，也不能确定是否其中的一块大陆静止不动，而另一块大陆正在远它而去；根据热点密度的分析可以看出，非洲板块静止不动了的3,000万年。据此可知，人们之所以认为非洲和南美洲曾经连在一起，是因为它们的某些地质特征相似。B项与文章的意思相符，因此B项为正确答案。
单选题 The hot spot theory may prove useful in explaining ______.
【正确答案】 D
【答案解析】[解析] 本题可参照文章的第3段。从中可知，热点区的重要性并不仅在于它们所起到的参照物作用；现在看来，它们还对推动板块在地球上移动的地球物理学的过程也产生了重大影响；当大陆板块漂移到热点区上方时，地壳深处涌出的物质会形成一个巨大的穹顶；随着穹顶不断增长，它会出现深深的裂缝；如此作用几次后，大陆可能会沿着这些小裂缝完全裂开，这样热点地区就导致了新大洋的诞生。于是，该热点便开始形成一个新海洋；因此，正如早期的理论解释了大陆的移动那样，热点或许可以解释大陆的易变性。据此可知，热点理论可以用于解释大陆的不稳定性，即热点可以促使形成新海洋。D项与文章的意思相符，因此D项为正确答案。
单选题 The passage is mainly about ______.
【正确答案】 C
【答案解析】[解析] 从文章第1段的内容可知，地球上散布着一百多个相互独立并且面积不大的火山活动区，地质学家称之为热点。随后说明了热点的特点。文章第2段说明了板块漂移理论，最后一句话指出：根据热点密度的分析可以看出——非洲板块静止不动了3,000万年；从文章第3段的内容可知，热点的重要性并不仅限于作为参照体系这一作用上，它们对推动板块地球上移动的地质物理过程也产生了重大影响；然后具体说明了热点如何促使形成了新海洋；从文章的最后一句话可知，正如早期的理论解释了大陆的移动那样，热点理论或许可以解释大陆的易变性。据此可知，本文主要讲的是热点理论在地质物理研究中的重要作用。C项与文章的意思相符，因此C项为正确答案。