Don't call me.l'm busy__my homework.a.do b.to do c.doing d./ 选什么?为什么?

Don't call me.l'm busy__my homework.a.do b.to do c.doing d./ 选什么?为什么?
Don't call me.l'm busy__my homework.a.do b.to do c.doing d./ 选什么?为什么?

Don't call me.l'm busy__my homework.a.do b.to do c.doing d./ 选什么?为什么?
doing
be busy doing 固定搭配

doing， 这个是固定用法，busy+doing something

c. be busy (in) doing sth. 忙于做某事