The poor dog was hurt ,luckily,it was ____at once
问题描述：
The poor dog was hurt ,luckily,it was ____at once
A.operated
B.operated on
答案：B
问：为什么不选B,求解释
打错了，为什么不选A
答
operate on sb：给某人做手术,介词on 不能丢的.这里用了被动语态.