20 The direction _______ a force acts is changeable.
问题描述：
20 The direction _______ a force acts is changeable.
A. at which B. to which
C. in which D. on which
答
选D.主要就是一个词组的介词搭配.力作用于方向:a force acts on the direction.在句子中 on which a force acts 做The direction的定语,=that\which a force acts on.act on ...作用于全句的意思是：力可以改变方向....