was后面加原型还是过去式

was后不接原形，也不接过去式，was后面可接以下三种形式。

1、接现在分词表示过去进行时

比如“I was doing homework at this time yesterday.”意思即“我昨天的这个时间正在写作业”

2、接过去分词构成被动语态

比如“He was scolded by his mother.”意思即“他昨天被他妈妈骂了”

3、接动词不定式表示过去将来时

比如“He was to go to bed when his mother came home yesterday.”意思即“昨天他妈妈就回家的时候他正准备睡觉”。

It be + 点时间 + before …还要过多久某人才做某事，因为before后面的从句是过去时，所以这里用was，因为这是发生在过去的事情

比如:

It was three years before he finished the work.

过了3年他才完成这项工作。

It will be three years before he finishes the work.

还要过3年他才能完成这项工作