在虚拟语气中,什么时候用would＋动词原形,什么时候用should＋动词原形

1.在if虚拟语气条件句,主句用would,could,sould,might+动词原形.一般总是用would不错,可以译为“就会”；有“可能会”、“也许会”之意时,用could,might较好；有“应该会”之意时用sould 较好.如：
If he had not been busy,he would/could/sould/might have helped you.他不忙的话,会/可能会/应该/也许会帮你忙的.
2.在“命令、要求、坚持、建议”等词后的that从句中用should＋动词原形,should可以省去.