1)在主语从句中的应用

It is demanded / necessary / a pity + that…等结构的主语从句，谓语动词用should 加动词原形，should 可省略。

It is 可用的词有三类that(should)dosuggested, ordered, required, proposed, demanded, requested, insisted等important, necessary, natural, imperative, strange等a pity, a shame, no wonder等

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，像order， suggest， propose， require， demand， request， insist， command， insist + (should) do等。例如：

I suggest that we (should) hold a meeting next week. 我建议下周召开个会议。

He insisted that he (should ) be sent there.他要求被派到那儿去。

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。

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

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。例如：

My idea is that we(should)get more people to attend the conference.我的想法是让更多的人来参加会议。

I make a proposal that we(should)hold a meeting next week.我提了个建议，下周我们开个会。