失活剂三氧化二砷的封药时间是
A．1周
B．24～48h
C．48～72h
D．2周
E．10d
参考答案：B
根据我国《建筑施工场界噪声限值》，混凝土搅拌机作业的昼间噪声限值为( )dB。
A．55
B．65
C．70
D．75
_________ they were here now, we would be able to celebrate their wedding anniversary.
A．Only if
B．If only
C．Because
D．When
