老师们好，麻烦有时间时帮我看看下面几个句子:

It's impolite to speak when you're eating.

It was considerate of you to whisper it to me in public.

It is quite necessary to react quickly to any emergency.

这几句话为什么用 to speak?

to react

to whisper？

为什么不用ing形式？

因为doing不是可以指一个事情么？

那 speaking when you're eating. 不就可以表达吃饭时说话这么一个事情是不礼貌的么？

为啥只能用 to speak表具体的一次行为呢？

我用speaking…当一个静态的事情看不行么？