在机场道面铺筑时，为了保障做面工艺有充分时间完成，在混凝土拌合物中加入()作为外加剂。
A.防水剂
B.早强剂
C.缓凝剂
D.速凝剂
参考答案：C
—I fell and hurt my leg just now.
—_____. [ ]
A. Be careful
B. It doesn't matter
C. I'm sorry to hear that
D. That's funny
