be excited +什么介词?虽然我看到公式是说+about但是为什么有句例句是：He is excited at the good news?//

as far as i am concerned, I would add another possibility to the confusion. excited by....
i am excited by his arrival
i am excited about the party tomorrow.
excited at is probably incorrect.

惯用法:
be excited about sth
be excited to do sth
与at搭配常见的形式一般和时间有关
eg: He was excited at first.
I am very excited at this moment
美式英语中不乏这样的用法
I feel very excited at the thought that in another week I'll be with you again on holiday.
考试和日常用法有很多不同，上课学的无非为了应试，看到多选有abt和at，选abt吧

be excited at “在.的影响下而激动
be excited about “关于某事而激动”
She is very excited about/at winning the first prize.
赢得首奖,她激动不已.
常可以互换

at 引导原因，可以跟在表示情绪、感情的形容词后，比如：
Mary was shocked at her grandpa's sudden death.
He is excited at the grand opening ceremony of the World Expo.