单项选择题
A.η<1 B.η>1 C.η=1 D.η=0
A.平板材 B.T型材 C.角钢 D.球扁钢
A.96.06 B.96.05 C.96.04 D.96.055
A.50.010 B.50.015 C.50.005 D.50.060
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