水变为水蒸气，主要改变的是[ ]

A．水分子本身体积变大

B．水分子质量变大

C．水分子间隔变小

D．水分子间隔变大

Jumping out of ____ airplane at ten thousand feet is quite ____ exciting experience. [ ]

A. 不填; the

B. 不填; an

C. an; an

D. the; the