________（49）A. More water was added to the planet

外语类 2020-04-28 00:24:28 已帮助人

________（49）

A. More water was added to the planet during several hypothesized large impacts from asteroids from the outer asteroid belt.

B.We know that the oceans existed as early as 100 million years after the formation of the Earth.

C.Still,the oceans only make up 0.023%of the Earth’s total mass.

D.Astronomers say Earth s water may have come from space.

E.The snow line is located in the outerasteroid belt,between the orbits of Mars and Jupiter.

F. Many geologists believe that the majority of Earth’s water generated through this process.

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答案：A
后一句：Comparing the isotope ratios of water on Earth and water from comets and asteroids has revealed that the majority of the Earth’s water comes from asteroids．通过把地球上水的同位素和小行星以及彗星上的水的同位素进行比较，发现地球上的水主要来自小行星。可以推断出，该句要讲述地球上的水与太空中小行星的关系，所以A选项正确。