在卧式镗床上镗削中小型工件的同轴孔系时，除穿镗法外，还可用调头镗来加工。
参考答案：对
—That must be Mr. John.
—No, it ______ be him. I saw him off at the airport half an hour ago.[ ]
A. may not
B. mustn't
C. can't
D. needn't
高炉煤气加热时，立火道空气过剩系数是（）。
A、a=1
B、a=1.15-1.2
C、a=1.20-1.30
D、a=1.5
