一、从结构上区别现在完成时：主语 + have / has + 过去分词 （肯定式）主语 + have / has + not + 过去分词 （否定式）Have / Has + 主语 + 过去分词 （疑问式）过去完成时：主语 + had + 过去分词 （肯定式）主语 ...