单项选择题
A.不应大于550kg/m3 B.不应大于320kg/m3 C.不应大于260kg/m3 D.不应大于300kg/m3
A.>2.5 B.>3.2 C.>2.1 D.<2.5
A.19mm B.26.5mm C.31.5mm D.37.5mm