防水混凝土抗渗性能试验的目的是用来检测混凝土硬化后的（）和混凝土抗渗标号（等级）。
参考答案：防水性能
It's time ________ supper.[ ]
A. to
B. in
C. on
D. for
We don't have ______ English lesson today. We have ______ Chinese lesson. [ ]
A. an; an
B. an; a
C. a; a
D. a; an
