英语语法小问题Who is to blame for the accident happened yesterday?这

问：我总是觉得她说的不对.不知道到底是什么 ?
答：应该老师是对的,你错了.
请比较以下两个句子
A, Who is to blame for the accident happened yesterday?错
B, Who is to blame for the accident seen yesterday? 对
我们还原两句话应该是：
A, Who is to blame for the accident which was happened yesterday?
B, Who is to blame for the accident which was seen yesterday?

A句 which was happend 很明显是错误的.
应该是sth happened 不能说 be happened. happen 没有被动语态.
B句用seen就对了表示的是昨天那个被别人看见的事故.
明白这句话的关键是 理解happen是没有被动的语态的词就好了
O(∩_∩)O~