获得驱力或衍生驱力
参考答案：
是经由学习，经由条件作用而获得的驱力。
24. —Mr Smith, ______ John ______ this week? A friend of his is coming to see him this afternoon.
—No. He is on holiday.
A．has; worked
B．is; working
C．did; work
D．does; work
如图所示，MN为空气和玻璃的界面，一束光线从空气入射到界面上的O点产生了反射和折射．请在图中画出法线并标明入射光线、反射光线及折射光线．
