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

________（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.