It is so small that it would take sixteen hours to fall half a mile in perfectly still air, and it does not fall out of moving air at all. (Passage 2)

【参考答案】

(云层中的水滴)是如此的小以至于在完全静止的空气中它要16小时才能降落半英里，并且在流动的空气中它根本不会降落。