1.主从句谓语动词的时态
(1)掌握主从句谓语动词的规范搭配:
主句 从句
与现在事实相反 would/情态动词过去式+do were (不分人称)/did
与过去事实相反 would/情态动词过去式+have done had done
与将来事实相反 would/情态动词过去式+do should do
如：
If the doctor had been available, the www.med126.com child could not have died.
There is a real possibility that these animals could be frightened, should there be a sudden loud noise.
(2)区分主从句表示的不同时间概念：
主从句谓语动词所指时间不同，这叫做错综时间条件句，动词形式应根据实际情况来调整。如：
Had it not been for the timely investment from the general public, our company would not be so thriving as it is.
(主句与现在事实相反，从句与过去事实相反)
Had Paul received six more votes in the last election, he would be our chairman now.
(主句与现在事实相反，从句与过去事实相反)
(3)识别事实和假设混合句：
Your math instructor would have been www.med126.com happy to give you a make-up examination had you gone and explained that your parents were ill at the time.
(句子前半部分为假设情况，而“父母病了”是事实)
I would have gone to visit him in the hospital had it been at all possible, but I was fully occupied the whole of last week.
(前半部分为假设，后半部分是事实)
