幽默在导游中可以起到（）的作用。
A.融洽关系
B.调节情绪
C.摆脱困境
D.寓教于乐
参考答案：A, B, C, D
铁丝在氧气中燃烧，生成的黑色固体质量大于参加反应的铁丝质量，用质量守恒定律的知识解释原因．
Blackmail is something that should never be _________, but it's easier said than done. [ ]
A. given out
B. given away
C. given up
D. given in to
