after doing?After (seeing) S.H.E,the fans became even more excited 为什么括号里用ing形式?

after+doing+sth对吗? BEFORE DOING和AFTER after do sth.还是after doing sth. 哪个短语对?：after doing ,after do ,after to do after doing s.th还是after do s.th?在书上看到两句话：1、After listening to it2、After they listen to it为什么一个是 doing s.th 一个是do s.th? 英语：after后面接doing? after after after after After after after After after after after after