在弯矩作用下,摩擦型高强度螺栓群的中和轴位于()
参考答案:螺栓群的形心
______no friction between the surface of the road and our feet, we could not walk at all.
A.If there was
B.Were there
C.Was there
D.There was
怎样搞好封炉操作?