be busy doing sth可以用work on替换吗?如果不能区别是什么?急用!

be busy doing sth可以用work on替换吗?如果不能区别是什么?急用! work on和be busy doing sth.的区别 be busy with sth 与be busy doing sth的区别 ,可以互换吗 忙于做某事为什么要用be busy doing sth 可以用be busy to do sth吗 be busy with sth.spend on sth.be busy doing sth.spend doing 用be busy doing sth.句型造句 be busy doing sth 和be busy to do sth 的区别 be busy with sth 与be busy doing sth的区别 be busy in doing sth be busy doing sth 例句 up to sth 的用法和be busy doing有什么区别吗 be busy doing sth/with sth