1.for 表示原因,与sorry, famous, punish, praise, thank, blame连用。

I am sorry for what I said to you. 我后悔不该对你讲那些话。

2.at 指情感变化的原因,意为“因听到或看到而……”。 He was surprised at the news. 听到这消息他大吃一惊。

3.from 指“外在的原因”,如受伤、车祸等。 He died from the wound. 他因受伤而致死。