be busy doing sth 其实也可以是 be busy (in) doing sth.意为忙于做某事.
例：I'm busy (in) doing my home work.
be busy to do sth.如果是 be too busy to do sth.
那就是too...to...结构了,可以这样用,太忙了以至于不能干什么.
但是如果没有那个too那就不能用to do只能用doing表示忙于做某事
busy 短语的用法常用的有两个：
be busy with sth 忙于做某事
be busy doing sth 忙于做某事
例如：
1.The plan for the new book is on ice at the moment.I've been busy with too many other things.
写那本新书的计划暂时搁一下,我一直忙于太多其它的事情.
2.I was busy with my children.
我忙于照顾孩子.
3.He is busy doing his homework.
他正忙着做家庭作业.
4.I am busy working.
我正忙于工作.
单独的busy +to do的结构是不成立的
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