最易发生幽门梗阻的溃疡是
A．胃窦部溃疡
B．十二指肠壶腹溃疡
C．幽门管溃疡
D．球后溃疡
E．复合性溃疡
参考答案：C
________ him before, I didn't recognize him.
A．Having never seen
B．Never seeing
C．Not seeing
D．Having not seen
推焦时产生的烟尘大约占总量烟尘量的（）%。
A.15
B.20
C.25
D.30
