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？
