问题补充：
问大家一个关于英语语法的问题..老师写了一个句子（I saw an old man knocked down by a car just now)意思是刚才我看到一位老人被车撞了...但我觉得既然是被撞,表被动不是应该为I saw an old man was knocked down by a car just now么..被动不都是be done结构么...但老师说的句子里为什么把be给省了?
答案：
I saw an old man (who was) knocked down by a car just now!定语从句,括号内可以省略!
