成人咽鼓管全长为:()
A.15mm
B.25mm
C.35mm
D.45mm
E.55mm
参考答案:C
Ladies and gentlemen, I have the great privilege____ introducing our speaker for tonight.
A.in
B.of
C.about
D.on
用砂轮磨削加工工具时,应使火星向()。