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  3. Our knowledge of the oceans a hundred years ago was confined to the two-dimensional shape of the sea surface and the hazards of

Our knowledge of the oceans a hundred years ago was confined to the two-dimensional shape of the sea surface and the hazards of

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问题     Our knowledge of the oceans a hundred years ago was confined to the two-dimensional shape of the sea surface and the hazards of navigation presented by the irregularities in depth of the shallow water close to the land. The open sea was deep and mysterious, and anyone who gave more than a passing thought to the bottom confines of the oceans probably assumed that the sea bed was flat. Sir James Clark Ross had obtained a sounding of over 2,400 fathoms in 1839, but it was not until 1869, when H. M. S. Porcupine was put at the disposal of the Royal Society for several cruises, that a series of deep soundings was obtained in the Atlantic and the first samples were collected by dredging the bottom. Shortly after this the famous H. M. S. Challenger expedition established the study of the sea floor as a subject worthy of the most qualified physicists and geologists. A burst of activity associated with the laying of submarine cables soon confirmed the Challenger’s observation that many parts of the ocean were two to three miles deep, and the existence of underwater features of considerable magnitude.
    Today, enough soundings are available to enable a relief map of the Atlantic to be drawn and we know something of the great variety of the sea bed’s topography. Since the sea covers the greater part of the earth’s surface, it is quite reasonable to regard the sea floor as the basic form of the crust of the earth, with, superimposed upon it, the continents, together with the islands and other features of the oceans. The continents form rugged tablelands which stand nearly three miles above the floor of the open ocean. From the shore line, out a distance which may be anywhere from a few miles to a few hundred miles, runs the gentle slope of the continental shelf, geologically part of the continents. The real dividing line between continents and oceans occurs at the foot of a steeper slope.
    This continental slope usually starts at a place somewhere near the 100-fathom mark and in the course of a few hundred miles reaches the true ocean floor at 2,500-3,500 fathoms. The slope contains steep, probably vertical, cliffs, and gentle sediment-covered terraces, and near its lower reaches there is a long tailing-off which is almost certainly the result of material transported out to deep water after being eroded from the continental masses.  
The H. M. S. Challenger expedition________.
选项 A、was devoted to dredging the ocean
B、was dedicated to laying submarine cables
C、gave the sea floor study disciplinary independence
D、obtained a series of deep soundings in the Atlantic
答案C
解析 事实细节题。H. M. S. Challenger expedition出现在第一段倒数第二句。该句指出，“挑战者”号舰艇的海底考察，把对海床的研究确立为一个值得研究的课题。C项表述与原文相符，故为答案。该段第三句话提到，直到1869年，皇家学会用英国“豪猪号”舰艇进行了几次巡航后，才在大西洋测得一系列海水深度，同时通过挖掘海底，取得了研究海底的首批样品。由此可知，挖掘海底和在大西洋测得一系列海水深度的是英国“豪猪号”舰艇，故排除A项和D项。该段最后一句提到，铺设海底电缆的热潮证实了“挑战者号”的观察结果。由此可知，铺设海底电缆的活动是“挑战者号”之后的活动，故排除B项。
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