焦比高时（）。
A、煤气中的N2含量升高
B、煤气中的CO+CO2含量增加
C、煤气中的CO含量减少
D、煤气利用率降低
参考答案：A, B, D
— Lucy is doing her homework.
— Let's ask Lily ______. [ ]
A. but
B. except
C. instead
D. instead of
_____speak more English in class?
A．You should
B．What about
C．Why don’t
D．Why not
