等角速万向节的基本原理是从结构上保证万向节在工作过程中,其传力点永远位轴交角的() The basic principle of the constant angular velocity universal joint is to ensure that its transmission point is always at the Angle of the intersection of two axes () in the working process of the universal joint from the structure. A. 平面上 In the plane B. 垂直平面上 On the vertical plane C. 平分面上 Split the surface D. 平行面上 On the parallel surface