[家教老师]

 

was

是 am, is 的过去式。用于第一人称单数（我 I ）和第三人称单数（如 she, he, it, this, that, Mike 等等单个人）作主语的句子，表达过去发生的事情。

wasn't

  是 was not 的缩写，是否定形式。

例如：I was 16 years old last year.
        She wasn't (was not) at home yesterday.
        Mike wasn't a doctor three years ago.
        It was Monday yesterday.

were

是 are 的过去式，用于复数(如they, we, you或两个以上的事物）作主语的句子中，表达过去发生的事情。

weren't

是 were not 的缩写，是否定形式。

例如:  They were at the playground just now.
         We were singing in the classroom an hour ago.
         You weren't at school  yesterday.
         The kids were very happy in the park last weekend.