If it should rain tomorrow,we will not do
谓语动词的虚拟形式
从句x05 主句
现在 动词过去式（be 多用were）x05 would / should / could / might + 动词原形
过去x05had + 过去分词x05 would / should / could / might + have + 过去分词
将来 动词过去式或 should / were to + 动词原形x05would / should / could / might + 动词原形