stop doing sth是“停止做某事”，doing是stop 的宾语，是要停止的动作，
stop to do sth 是“停下来开始做某事”，to do是stop的状语，表示目的，是要开始做的事情，例如：
1、The two girls stopped talking when they saw me.
那两个女孩一见到我就停止了讲话。
2、The two girls stopped to talk to me when they saw me.
这两个女孩一看到我就停下来和我讲我。
Stop …from doing…表示“阻止…不做某事”，from 可以省略。例如：
We must stop him from going to swim in the river.