该课程教学中采用了以下哪种方法 ( )

单项选择题凸轮与从动件接触的运动副属____ A、移动副 B、转动副 C、高副 D、螺旋副

单项选择题What is the meaning of “serve its purpose” and “every step of the way” in the sentence “From animal skin to linen, from cambric (麻布) to silk and cotton and to the various kinds of materials today, innovation served its purpose every step of the way.”