This shirt is mine/XXX's.这件T恤是我的/XXX的。或者 It's mine/XXX's.
This is my shirt.This is his/her shirt.This is Tom's shirt.都可以
It is mine。
那要看是谁的了，如果是我的就是it's mine你的就是it's yours 他的她的它的就是it's his her its
