The doctor was busy ____ on the boy at that time.B.to operate D.operatingB为什么错了?
问题描述：
The doctor was busy ____ on the boy at that time.
B.to operate D.operating
B为什么错了?
答
.固定词组~~~
答
be busy doing sth 忙于做某事
答
be busy doing sth是固定词组
答
be busy doing是 固定搭配哦