A.7.8mm B.78mm C.16.7mm D.83mm
A.正方形截面最费料 B.圆形截面最省料 C.空心圆截面最省料 D.三者用料相同
A.9.38MPa B.5.63MPa C.3.75MPa D.11.26MPa
A.92.4kN B.140kN C.104.3kN D.150kN
A.6kN·m B.6.25kN·m C.9kN·m D.12kN·m
