英语主语从句中的虚拟语气

在表示建议、要求、命令等含义的主语从句中，谓语动词一般使用拟语气，其构成方式为“动词原形”或者“should+动词原形”。

常见句型有：
It is necessary that … 有必要……, ……必须
It is imperative that … 必须……, ……是紧要的
It is important that … 重要的是……, ……是很重要的
It is essential that … 必须……, ……是必要的
It is advisable that … 最好……, ……是理想的
It is ordered that … 根据命令……, 人们要求……
It is better that … 最好……
It is proposed that … 人们建议……
It is desired that … 最好…… 需要……
It is requested that … 人们要求……
It is suggested that …有人建议……
It is demanded that … 根据要求……
It is decided that … 已经决……
It is arranged that … 业已安排……
It is recommended that … 有人推荐……
It is required that … 有人要求……

例句：
It is suggested that the meeting (should) be put off.
人们建议会议延期。
It is necessary that the letter (should) be delivered right away.
有要立即把信寄出去。
It is demanded that everything (should) be ready within 3 days.
根据要求，要在日之内一切准备就绪。