be busy+in还是on还是at还是不加
问题描述：
be busy+in还是on还是at还是不加
答
be busy in doing sth（正忙于做某事）,一般将in省略了,就写成be busy doing sth了
没见过be busy on或者at的,只有be busy with sth,意思和be busy in doing sth一样,如：
1.be busy with sth
例如:I am busy with my homework!
2.be busy in doing sth
例如:I am busy in doing my homework!