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? 明白了么?