bought 过去分词作定语. = which was bought为什么不能用was bought?因为用was,带有谓语动词，就是句子了，定语从句。 而先行词the book做定语从句的主语是不省略that/which德所以，要么用过去分词作定语，bought for...要么用定语从句作定语 the book that/ which was bought for me...先行词做作定语从句的宾语可是省略that/which例如 the book（that/ which）my father bought for me...欢迎追问