TOEFL Reading: ETS-TOEFL阅读机经 - 3L6G5VVB97ME54G6L$

According to paragraph 3, why is water able to move so freely on Earth? A. Earth's temperatures are such that water exists in solid, liquid, and gas forms. B. Earth is large enough to be geologically active and for its gravitational field to hold an atmosphere. C. Earth's surface allows river valleys to develop across the landscape. D. Earth has active winds that blow across seas and oceans, causing fluid movements.