在英语中，“before”是一个介词，后面通常接名词、代词、动名词或从句。如果“before”后面接动词，通常需要使用动名词形式，即“-ing”形式。例如：
“I had seen the movie before”应该改为“I had seen the movie prior to”。但是，“before”后面也可以接一个完整的句子，此时需要使用动词的正确时态和语态。例如，“It was better to stay home before it rained”应该改为“It was better to stay home before it had rained”。
以下是before的例句：
It will be midnight before we finish the work. (before作为连词)
We had walked some distance before we found the post office. (before作为连词)
He had not waited long before the bus arrived. (before作为连词)
I shall do it before you leave today. (before作为连词)
It was midnight before the phone rang. (before作为连词)
He had done most of the work before he left his job. (before作为连词)
I must write it down before I forget it. (before作为连词)
Before she left, she had finished the work. (before作为连词)
They had to wait for a long time before they were ready. (before作为连词)
It will be some time before they are ready. (before作为连词)
以上就是before后面动词什么形式的问题解答，总的来说，“before”后面动词的形式需要根据具体的语境来判断。
