单项选择题
A.R =41d2(kN)B.R =41d2(kg)C.R =27d2(kN)D.R =27d2(kg)
A.R =13.5d2(kN)B.R =13.5d2(kg)C.R =15.3d2(kN)D.R =15.3d2(kg)