My grandpa [ lay ] down and had had a good rest .为什么lie 用过去式?

应该是My grandpa [ lay ] down and had a good rest .这里主语是My grandpa 有两个谓语部分即 [ lay ] down & had a good rest .根据同一主语的两个谓语部分保持一致的原则.lay 与had保持一致,故用过去式lay