it'shightimethat后面可接两种形式,+sbdid或者sbshould（这个should不能省）,可为什么同样是这种句型的其他句子,should就能省略,比如it'apity+that（should）+动词原型?,

Question

it's high time that 后面可接两种形式,+sb did或者sb should（这个should不能省）,可为什么同样是这种句型的其他句子,should就能省略,比如it' a pity +that （should）+动词原型?,

Answer 1

It is (high)time (that)sb did/should do 是句型所要求的,无理由可讲；而It is a pity that...句型可以用陈述语气也可用虚拟语气,用should表示竟然,should可省略：
It is a pity that you didn't come.It is a pity that it comes at such a cost.
It is a pity that he （should ）give up this chance.真遗憾,他竟然放弃了这个机会.
It is a pity that such a thing (should) happen in your class.这种事竟然发生在你们班上,真是遗憾.