[单项选择]

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, scien
A. the origin of the earth
B. the origin of the ocean
C. the history of the earth
D. the forming of the earth’s crust

最新试题

• ●    维生素D缺乏性手足搐搦症发生喉痉挛表现描述错误的是（）
• ●    [单选题]判断题 简单 生产经营单位应当将事故隐患排查治理情况向从业人员通报。
• ●    [判断题] 贷款申请是否受理基于对客户或项目的初步判断，在贷款收益与贷款安全的权衡上，应坚持将贷款安
• ●    能燥湿利水的药物是（）
• ●    [填空题](74991)青藏软卧车采用一台制冷量为()的车顶单元式空调机组，安装在一位端顶部；车内两
• ●    [单选题]危险货物（）办理站界内搬运或途中装卸。