与普通钢筋混凝土结构相比，预应力混凝土结构大大推迟了（）时间。

A、混凝土裂纹出现

B、钢筋被拉断

C、混凝土被压坏

D、网状裂纹出现

— Don't worry. Your father is coming to help you.     

— _____ he doesn't come? [ ]

A. What about

B. Why not

C. What if

D. What for