下面这些金属与铜合金最容易遭受腐蚀的是（）。
A.铁
B.锌
C.铝
D.镁
参考答案：D
—Be quiet, Mr Smith is coming.
—Don't worry. It _____ be him. Mr Smith is much taller. [ ]
A. mustn't
B. must
C. can't
剧场座椅与墙壁间的通道的边界层宽度为（）cm。
A．0
B．9
C．20
D．29
