had 是行为动词的过去式：过得,享受,替代的助动词是did.
had done,had.
---He had finished his work before yesterday. ----So he had (finished his work).还是不咋懂，说简单点，我英语特差have, 有很多词义和功能，不同的情况要不同地运用它。have sth = 有，拥有，所有。很特殊的用法。和其他行为动词一样：He has a new car. --- So he does.也可以说：----So he has.但除此意思外，必须作为普通的行为动词使用，否定、疑问、替代都得用相应的助动词。--- He had his breakfast. --- So he did. = had his breakfast. = had...= ate, 吃不可说：---So he had.