减水率
参考答案：
在混凝土坍落度基本相同时，基准混凝土和受检混凝土单位用水量之差与基准混凝土单位用水量之比。
I wrote a letter of complaint, and the airline has promised to _____ the matter.
A．look up
B．look into
C．look through
D．look for
