1、忙于做某事
...B解析分析：少量的“be+形容词”后面的动词要用doing形式，常见的有be busy doing sth(忙于做某事)，be worth doing(值得做)。(延伸)be busy with sth(忙于做某事)和be busy doing意思相同。
2、忙于
...get off离开; 动身be busy doing sth忙于(做)...pick up拾起, 捡起; 抬起 ...
3、忙于干某事
做完某事 be busy doing sth. 忙于干某事 go on doing sth. 继续干某事 .
4、忙于做
... be busy with 忙于... be busy doing sth 忙于做... by bus /car / plane 乘公共汽车/汽车/飞机 ...
be kept busy doing sth被迫忙于
be e busy doing sth忙于
doing be busy doing sth忙于干某事
be busy in doing sth忙于做某事
be busy doing sth sth忙于
playing be busy doing sth忙于做某事