单选题 {{B}}Passage Three{{/B}}
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.
单选题 This passage mainly talks about ______.
【正确答案】 B
【答案解析】根据第一段第一、二句，Many theories about the origin of the ocean have been proposed by scientists．The most widely accepted one is that...作出该项选择。
单选题 According to the passage, the earth in its very early period was ______.
【正确答案】 A
【答案解析】根据第一段第二、三句，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作出该项选择。
单选题 It can be learned from the passage that about four billion years ago ______.
【正确答案】 B
【答案解析】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。
单选题 In the last sentence of the second paragraph, "the higher places on earth" refers to ______.
【正确答案】 D
【答案解析】根据第二段最后一句及第三段第一句，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可知“较高的地方”不可能指选项B和C；选项A文中未提及。
单选题 According to the passage, which is true about the ocean?
【正确答案】 A
【答案解析】选项A符合第二段内容。选项B与原文不符；选项C与第三段最后一句及最后一段不符；选项D与原文第二段最后一句不符。