leavesthforsb还是tosb,

buy sth for sb.
supply sth to/for sb的意思是"为某人提供某物,在这里supply是动词
to do sth 要某人干某事 ask sb for sth 向某人要某东西
九年级英语-itis adj of-sb to-do-sth
it is adj for sb to do sth.