动词的过去式用于一般过去时且该动词做句子谓语时;
而动词的过去分词用于其他情况,如被动语态,完成时态,非谓语形式等;
如:do/did/done
1.He did something bad just now.
2.Something bad was done by hime just now.
3.He has/had done something bad.
4.You must have your homework done before tomorrow.