产生温室效应的主要气体是()
A.CO2
B.NOX
C.SO2
D.H2S
E.CO
参考答案:A
— What do you think of the concert?
— There was nothing special; it was only____. [ ]
A. average
B. usual
C. normal
D. common
循环水运行前的预处理包括清洗和()。