is,are was were的区别?

did是助动词do和does的过去式,而was/were是be动词am、is/are的过去式.
一个句子中,如果没有be动词,发生动作要用助动词do或does.
例如：I am a student.问句是：Are you a student?有be动词所以直接用are提问.
I worked in an international company 2 years ago.
句中没有be动词,所以要用助动词代替,问句是：
Did you work in an international company 2 years ago?

is 表单数
was is的过去式
are 表复数
were are的过去式

were和was的区别 is are
were是are的过去式 表示复数.
was是is 的过去式 表示单数.
eg: There was a slide on the playground.
There were many trees on the playground.
children were happy yesterday.
Amy was hungry yesterday.