未然法烟气中CO含量为（）％。
A.40～60%
B.50～70%
C.60～80%
D.70～90%
参考答案：C
---Can you come on Monday or Tuesday, John?
---I’m afraid _______ day is possible. I will be very busy on those two days.
A．every
B．some
C．either
D．neither
白喉毒素
