虚拟语气中的SHOULD有的时候,SHOULD可以省略,但是什么时候可以省略,什么时候不能省略呢?请回答清楚啊,答的好的我给加分!

1） It is demanded / necessary / a pity + that…结构中的主语从句的谓语动词要用should 加动词原形, should 可省略.
句型：
(1)suggested
It is (2)important that…+ (should) do
(3) a pity
(1)suggested, ordered, proposed, required, demanded, requested, insisted； + (should) do
(2)important, necessary, natural, strange
a pity, a shame, no wonder
(3)It is suggested that we (should) hold a meeting next week.
It is necessary that he (should) come to our meeting tomorrow.
2）在宾语从句中的应用
在表示命令、建议、要求等一类动词后面的从句中.
order, suggest, propose, require, demand, request, insist, command, insist + (should) do
I suggest that we (should) hold a meeting next week.
He insisted that he (should ) be sent there.
注意： 如suggest, insist不表示"建议" 或"坚持要某人做某事时",即它们用于其本意"暗示、表明"、"坚持认为"时,宾语从句用陈述语气.
The guard at gate insisted that everybody obey the rules.
判断改错:
（错） You pale face suggests that you (should) be ill.
(对) Your pale face suggests that you are ill.
(错) I insisted that you ( should) be wrong.
(对) I insisted that you were wrong.
3）在表语从句,同位语从句中的应用
在suggestion, proposal, idea, plan, order, advice等名词后面的表语从句、同位语从句中要用虚拟语气,即（should）+动词原形.
My idea is that we (should) get more people to attend the conference.
I make a proposal that we (should) hold a meeting next week.