选C
虚拟语气：1.与事实相反的假设：
虚拟条件句：If +主语+动词的过去式（be动词用were）
主句：主语+should或would或could或might+动词原形
例句：If I were you ,I should seize the chances to go abroad.
If I had time ,I would attend the meeting.
2.与过去事实相反的假设：
虚拟条件句：If +主语+had+过去分词
主句：主语+should或would或could或might+have+过去分词
例句：If you had taken my advice,you would not have failed in the exams.
3.与将来事实相反的假设：
虚拟与条件句：（1）If +主语+动词过去式
（2) If +主语+were to+动词原形
（3）If +主语+should+动词原形
主句：should或would或could或might+动词原形
例句：If you came tomorrow,we would have the meeting.