为什么不用has 时间作主语不是用单数吗?The last thirty years have seen the gre

为什么不用has 时间作主语不是用单数吗?The last thirty years have seen the gre the last thirty years have seen the greatest number of The last thirty years have seen the greatest number of laws the last 19 years has seen the great change that have happed The last thirty days has seen a World Cup like no other 中的 l What --------- to China during the last thirty years?用happen the last few years have seen.是固定搭配吗?这算拟人吗? The secretary and principal作主语为什么是单数? have to 的主语要是第三人称单数形式的话,have用不用变成has呢? The last few years has seen great changes in this country对吗 They have seen the film yesterday.(用She做主语) The last thirty years----the greatest number of laws stoppin