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  3. Many theories about the origin of the ocean have been proposed by scientists. The most widely accepted one is that the earth at

Many theories about the origin of the ocean have been proposed by scientists. The most widely accepted one is that the earth at

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问题     Many theories about the origin of the ocean have been proposed by scientists. The most widely accepted one is that the earth at some time in its very early history became hot enough to melt the materials from which it was formed. While in this molten state, lighter rock-forming materials (造岩材料) floated on the surface of the heavier ones. Then, between four and a half four billion (十亿) years ago, the molten earth cooled sufficiently to form a crust of rock that was many miles thick.
    Surrounding the earth was an unbroken canopy of clouds miles thick and made up mostly of water vapor. Rain falling toward the still-hot earth was heated to steam and rose to the clouds again. After many millions of years, as the earth continued to cool, its surface temperature fell below the boiling point of water. Rainwater could now remain on the earth, covering its whole surface except for the higher places on earth that had been formed from the lighter rock materials.
    In 1970, scientists had pieced together evidence that the lighter rock materials had formed one huge continent by a vast ocean. Then, about 200 million years ago, the great continent began to break up, the pieces moving slowly apart.
    The onrushing waters of the single huge ocean now entered and filled the spaces between the separating continents--and became the several oceans and seas we know today.
It can be learned from the passage that about four billion years ago ______.
选项 A、the earth was in molten state
B、the earth surface temperature was above 100℃
C、the earth surface temperature was below 100℃
D、rain water could remain on the earth
答案B
解析 根据第一段最后一句及第二段内容可知，雨水在地表温度降到水的沸点以下才能停在地表，由此可知大约在四十亿年前，地表温度应在沸点以上。
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