the action of the medicine on the skin. 该药对皮肤的作用
Photographs are produced by the action of light on film. 光对底片发生作用从而产生照片。
Is your machine still in action? 你的机器还在运转吗?
The rules will be brought into action tomorrow. 章程从明天开始生效。
We studied the action of the digestive system. 我们学习了消化系统的作用。