be busy to do sth.
忙于做某事
be busy doing
忙于做某事
意思上没有区别
通常来说固定短语只有be busy (in) doing sth.或者be busy with sth
如:
He was busy (in) preparing for the exam.
He was busy with his work and didn't notice his mother come in.
be busy to do 是没有的,但是我们可以用be too busy to do sth,表示“太忙不能(去)做……”,如:
I'll be too busy to come to the party.
She was always too busy to listen.
be busy to do sth.忙于做什么事和be busy doing忙于正在做