同学你好，该知识点来自沪江网校《零基础直达BEC商务英语高级四项全能实战签约【现金奖励班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学你好！很高兴回答你的问题～
首先这些词都是be动词 am,is are的过去式,当句子的时态是过去时时需要使用
am/is— was    am not/ is not— wasn't       are— were       aren't— weren't
(1)当句子主语是第一人称或第三人称单数，且句子时态是过去时，用was或者是 wasn't
when I was a little girl I always went there by train.
When she was a little girl she always went there by train.
There wasn't a thing to eat.  这里没什么可吃的。
(2) 当主语是第二人称或当主语是复数，且句子时态是过去时，用were 或者是weren't
We were good friends but now we are not. 我们那时是好朋友，但现在不是了。
You were out of office yesterday, right? 你昨天不在办公室，对吧？


祝学习愉快！