由于机场下雪跑道的摩檫系数变化（）时，为雪情的重要变化。
A.约0.5
B.约0.05
C.约0.01
D.约0.1
参考答案：B
—What do they do?
—_________. [ ]
A. They are actors.
B. They are Chinese.
C. They like movies.
何谓物理脱色？何为化学脱色？
