Question

I didn’t know his telephone number. ________ it, I ________ then.

A. Had I known; would ring him up    B. Should I know; would have rung him up

C. If I knew; would ring him up    D. Had I known; would have rung him up

Answer

D

【解析】考查虚拟语气。由“I didn’t know his telephone number.”可知，是对过去的假设。If 从句用had done，主句用would/could/might have done。而if从句中省略了if，把had提到句首，故选D。

【名师解析】虚拟语气在if引导的条件句中的用法：

一、1. 表示与现在事实相反的虚拟条件句

If+主语+动词的过去式（be用were）, 主语+would(should/could/might)+动词原形

1)If I were you, I should study English.

2)I would certainly go if I had time.

2. 表示与过去事实相反的虚拟条件句

If+主语+had done, 主语+would（should/could/might）+have done

1)If you had taken my advice, you would not have failed in the test.

3.表示与将来事实相反的虚拟条件句

If+主语+should（were to）+动词原形/动词的过去式, 主语+would（could/should/might）+动词原形

1)If it were to rain tomorrow, the meeting would be put off.

二、 错综时间虚拟条件句 即条件从句与主句所指时间不一致，如从句指过去，而主句即指的是现在或将来，此时应根据具体的语境情况，结合上面提到的三种基本类型对时态作相应的调整。

1）If it had rained last night, the ground would be wet now.

要是昨晚下过雨的话，现在地面就会是湿的

一般来说虚拟语气中的混合时态的句子都有具体的时间词来进行提示的，比如说

2）You would be much better now if you had taken my advice. 假若你当时听我的话，你现在就会好多了。（从句与过去事实相反，主句与现在事实相反。）

3）If we had arrived at the shopping mall earlier, we would get more gifts now. 如果我们早点来商场的话（过去的时间虚拟），我们现在就可以拿更多的礼物了（现在的虚拟）。 这是两个不同时间的虚拟语气，有相应的时间词来提示的，now来提示后句的时间是现在而不是和前面一样的过去。

4）If you had worked hard，you would get higher marks. 如果没有明确的时间状语，可以根据语境而定。如这个句子，很明显是在说过去要是认真点，现在就不会分数低。从句与过去事实相反，谓语用had done；主句与现在事实相反谓语用would do。

三、if省略句。在条件句中可省略if, 把were, had, should提到句首，变为倒装句式。如：

1)If I were you, I would study harder. → Were I you, I would study harder.

2)If you had come earlier, you would catch the bus. → Had you come earlier, you would catch the bus.

3)If it should rain tomorrow, we would not go climbing→ Should it rain tomorrow, we would not go climbing.

注意：若省略的条件句中的谓语动词是否定形式时，不能用动词的缩略形式。

如：我们可以说：Were it not for the expense, I would go abroad now.

但不能说：Weren't it for the expense, I would go abroad now.