虚拟语气if的三种用法

1、表示与现在事实相反的情况：从句：If+主语+动词一般过去时(Be动词用were)。主句：主语+ should/would/might/could+do。2、表示与过去事实相反的情况：从句：If+主语+had+done。主句：主语+should/would/might/could+have done。3、表示与将来事实相反：从句：①if+主语+were to do。②if+主语+should+do。③if+主语+动词一般过去式（be动词用were）。主句：主语+should/would/might/could+do。