1.用在decide,decree,demand,insist,move,order,prefer,propose,recommend,request,require,suggest,vote等动词之后的that从句中,一律用（should）+be动词原形
2.用在advisable,appropriate,desirable,essential,fitting,imperative,important,impossible,necessary,obligation,proper等形容词之后的that从句中,be哦那个词用原形
3.用在decision,decree,demand,instruction,order,requirement,resolution等名词之后的that从句中,be动词也用原形
这个是be动词的虚拟形式,只要记住就可以了!