在主语从句中用来表示惊奇、不相信、惋惜、理应如此等语气时，谓语动词要用虚拟语气“(should) +do”，常用

的句型有：
　　It is necessary (important, natural, strange, etc.) that …
　　It is suggested (requested, proposed, desired, etc.) that…

 should型虚拟语气只从句中需固定使用“should + 动词原形”的谓语形式。
值得一提的是，在以上五种情况下用虚拟语气是美国英语和英国英语共同的特色，所不同的是美国英语通常省掉should，而英国英语通常保留should。主要包括以下三类：
1. It + be + adj./n./-ed +that +(should) do
2. 主语+动词+ that +(should) do或者同词根名词构成的同位语从句
3. in case(万一…)/ lest(以免…)/ for fear that (以免…) +(should) do
注：当从句中谓语动词表示过去或者已经完成的动作时，从句谓语根据具体情况可用 （should）have done 的形式
It + be + adj./n./-ed +that +(should) do
在“It is important (strange，natural，necessary) that…”这类句型里，that所引导的主语从句中的谓语动词常用 “should十动词原形”结构，表示某事是“重要”、“奇怪”、“自然”、“必要”、“遗憾”等意义。
表重要:important,urgent，vital
表必要：necessary，essential，imperative
表自然（会）：natural，proper，right，advisable，desirable，no wonder
表奇怪：strange，surprising，amazing
表遗憾：pity,regret,regretable
It is important that every member (should) inform himself of these rules. 重要的是每个成员知道这些规则。
It is most urgent that the patient should get to hospital.那病人应该马上送医院。
It is vital that we should be kept informed of all developments.重要的是我们必须熟悉所有的发展情况。
It is necessary that our college students（should）master a foreign language．我们大学生掌握一门外语是很必要的。
It is natural that he should get angry.他会生气是很自然的事。
It is proper that one who works hard should be successful.努力的人会成功，这是合理的。
(It is )no wonder that such a naughty boy should be punished.这样顽皮的孩子会受到惩罚，这是没什么好好奇的。
It is a pity/a regret/regrettable  that he should be so rude.他这么粗鲁，真令人遗憾。
It is requested that the cloth（should ）be woven at once．下令马上织这种布。
It is desired that the bridge（should）be built intwo years．要求两年内建成这座桥。
It has been decided that the meeting（should）be heldtomorrow已经决定会议明天举行。
主语+动词+ that +(should) do
在表示建议、要求、命令,规定、主张等的动词宾语中。用“should + 动词原形”形式。

表建议：suggest，recommend，advise，propose，move（提议），urge(呼吁）

要求：ask，require，request，desire，demand，insist
命令：order，command
规定：rule，regulate，stipulate
主张：maintain
The old peasant suggested that a reservoir（should）be built at the foot of the hill，那位老农建议在这座山脚下修座水库。
“The experiment had failed！”“I suggest you（should）try again．”“实验失败了！”“我提议再试一试。”
I desire that you（should）finish thetask today．我希望你今天完成这项任务。
They requested（demanded）that everyone（should）attend the
meeting ontime．他们要求大家准时出席会议。
He proposed that we（should）visit their schoolnext week．他提议我们下周参观他们的学校。
The captain ordered（commanded）that his soldiers（should）go on tothefront．上尉命令他的战士继续开往前线。
The boy insisted that he（should）go back alone．这孩子坚持要一个人回去。
I demand that he (should) answer me immediately. 我要求他立刻答复我。
注：这类词的形容词和名词所带的定语从句及名词性从句也用should+ 动词原形，如：
Their demand is that their wages be increased by 20%.  他们要求工资增长20%。                           
They made the suggestion that he leave at once. 他们提议马上离开。
凡是主句中有以suggest，proposal，order，idea，plan，news，motion，demand等名词后面所带的表语从句或同位语从句中，其谓语部分的should可以省略。例如：
Xiao Wang's suggestion is that we（should）play basketball after school．小王建议放学后打篮球。
My idea is that our class meeting（should）be held next week．我的意见是下周开班会。
I agree to your motion that we（should）go swimmingthis afternoon．我赞成你的建议，今天下午我们去游泳。
They are discussing your proposal that we（should）visit the Great Wall of China tomorrow．你建议我们明天去参观长城，他们正讨论。
in case(万一…)/ lest(以免…)/ for fear that (以免…) +(should) do
He took a raincoat with him lest it （should） rain.他怕下雨便带了一件雨衣。
She put a wool blanket over the child for fear that/lest he （should） catch a cold.

她把一条毛毯盖在孩子身上，以防他感冒。
Keep quiet in case you（should）interrupt him when he is busy．要保持安静，以防打扰他。
She is now studying for fear that she（should）fail in English．她现在很勤奋，生怕英语不及格。
You must wake him early lest he（should）be late for school．你务必早点叫醒他，以免他上学迟到。