在主语从句中，谓语动词的虚拟语气用“should + 动词原形”的结构，表示惊奇、不相信、理应如此等。如：
It is necessary(important, natural, strange, etc.)that we should clean the room every day.
It was a pity (a shame, no wonder, etc.)that you should be so careless.
It will be desired(suggested, decided, ordered, requested, proposed, etc.)that she should finish her homework this afternoon.
注意：这种从句表示的是事实。如果说人对这种事实表现出惊奇的情感，就可用虚拟语气。反之，如果不表示惊奇等情感，that从句也可用陈述句语气。如：
It is pity that you can't swim.
