单项选择题
A.90×6,ix=27.9mm,imin=18mm B.80×6,ix=24.7mm,imin=15.9mm C.75×6,ix=23.1mm,imin=14.9mm D.63×6,ix=19.3mm,imin=12.4mm
A.0.682 B.0.836 C.0.820 D.0.810