matter一般带有贬义色彩,只“小事,麻烦的事”
event 大事,事件（如911event）
affair一般指较大的事或是男女韵事
thing泛指
business公事,正事
因虽然都有“事情”一意,但是用法语境截然不同
例句如下：
what's the matter (with you)?
what's the matter with your watch?
All we americans learnt a lot from the 911 event.
It is said that his love affair with that young girl was found by his wife.
My son's birthday party is a big affair in our family.
This case is too easy for me!
please check that case now.
What are those things over there?
I went to Tokyo for business.
（今天刚给学生上课回来,刚好讲到这里所已很清楚）