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 / were to do
如：If the doctor had been available, the 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 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)
2.名词性从句的虚拟形式
名词性从句是指宾语从句、主语从句、表语从句和同位语从句。从句的谓语动词需用(should+)动词原形表示虚拟。考生应熟悉：
(1)下列动词做谓语时，that宾语从句中的动词用虚拟形式：
desire, advise, recommend, command, direct, order, ask, demand, request, require insist, maintain, move, propose, prefer, urge, vote。如：
In the past men generally preferred that their wives work in the home.
I move that he be discharged for his serious mistake.
(2)下列形容词和分词做表语或补语时，that主语从句中动词用虚拟形式：
advisable, desirable, insistent, preferable, urgent, appropriate, compulsory, crucial, essential, imperative, important, necessary, obligatory, possible, probable, proper, vital, advised, arranged, commanded, demanded, desired, ordered, proposed, recommended, requested, required, suggested。如：
The board deem it urgent that these files should be printed right away.
It is essential that all these figures be checked twice.
(3)下列名词接同位语从句或表语从句时，从句中动词用虚拟形式：
insistence, preference, recommendation, suggestion, proposal, motion, desire, requirement, request, order, necessity, importance, regulation, rule, resolution, understanding。如：
John Wagner’s most enduring contribution to the study of Afro-American poetry is his insistence that it be analyzed in a religious, as well as worldly, frame of reference.
They keep telling us it is of utmost importance that our representative be sent to the conference on schedule.
