He usually does his homework two hours in the evening. [ ]
A. about
B. to
C. in
D. for
答案:D
It wasn't until nearly a month later________I received the manager's reply .
A.since
B.when
C.as
D.that
表面曝气机叶轮浸没深度一般为(),浸没深度大时提升水量大,但能耗也会增加。
A.5~10mm
B.10~50mm
C.10~100mm
D.50~100mm