三种情况，(1)对过去，从句had done主句would/could/might/have done(2)对现在，从句：did /were主句：would/could/might do(3)对将来，should do/were to do/did.从句，更上一个一样。注意，“主将从现”原则。
1．名词性从句：
demand/suugest/order/insist/propose/request/ask/advise/prefer/mand/desire that…
They demanded that the aggressor troops (should) be withdrawn immediately.
由insist引导的宾语从句可以虚拟也可以不虚拟：
He insisted that he was right.坚持认为
He insisted that we should agree with him.坚持某事
由suggest引导的宾语从句可以虚拟也可以不虚拟：
His white face suggests that his not healthy.表明
He suggested that we have a rest.建议
If I could only see him once!
If only I had listened to your advice. 很明显，这种句型省略了主句
2．其他状语从句中：
as if/as though/even if…
Tom looked sad as if he had heard bad news.
I won’t lend you any money even I had money.
三种情况，(1)对过去，从句had done主句would/could/might/have done(2)对现在，从句：did /were主句：would/could/might do(3)对将来，should do/were to do/did.从句，更上一个一样。注意，“主将从现”原则。
一、有两种含有 but 的短语需要用虚拟语气，意思都是“如果没有,要不是,若非”
1. 复合介词 but for，如：
They would have resisted but for lack of courage.
若非勇气不足，他们会反抗的。
2. 复合连词 but that，如：
They would have resisted but that they lacked courage.
如果当时不是缺乏勇气的话，他们会反抗的。
二、if 和 but for/that 在意思上正好相反，比如上面的句子用反义句表示，就可以用 if 改写：
They would have resisted if they were full of courage.
如果他们勇气十足的话，他们就会反抗的。
跳层虚拟句（即句子一半为虚拟，另一半为陈述语气；but前句用虚拟而or/otherwise后句用虚拟） (but)
He would put on weight, but he doesn't eat much. (与现在事实相反)
He would have put on weight, but he didn't eat much. (与过去事实相反)
(or, or else, otherwise)
I fet where I read the article, or I would show it to you now. (与现在事实相反)
Mary couldn't have received my letter, otherwise she would have replied before now. (与过去事实相反)
but for 要不是。。。
要不是你迟到了，我们早就可以到
时态往后退一个，将来退过去将来，现在退过去，现在完成退过去完成，过去退过去完成，
1．虚拟语气在条件句中的用法
（1）若表示与现在事实相反的假设,则条件从句中用过去式,主句中用过去将来式（would,should,could,might + 动词原形）；若表示某事将来实现的可能性不大,则条件从句中用should + 动词原形也可用“were to+动词原形”或用过去式动词.如：
I would certainly go if I had time．（现在）
If it should rain,we wouldn”t go out.（将来）
If I knew German,I would read the paper to you．（现在）
If he were here,we could ask him．（现在）
（2）若表示与过去事实相反的假设,从句中用过去完成式,主句中用过去将来完成式（should,would,could,might + have + 过去分词）.如：
If I had set off a little earlier,I would have caught the train．
She would / might have e if she hadn”t been so busy．
If I hadn”t taken your advice,I would have made a bad mistake．
If only you hadn”t told him the news．
（3）含有虚拟语气的条件状语从句中,如有had,should,were 这三个词的话,在正式或书面语言中可将if省略,再将句子的主语和谓语动词实行全部倒装或部分倒装.如：
Had they time（=If they had time）,they would certainly e and help us．
Should it be fine（=If it should be fine）,we would go for an outing．
Were I go（=If I were you）,I would go．
（4）若主句从句所指的时间不一致,即条件从句表示与过去事实相反,主句表示与现在事实相反；或者条件从句表示与现在事实相反,主句表真实情况,则从句中应采用与具体时间相对应的虚拟形式.如：
If it had rained last night（过去）,It would be very cold today（现在）．
If I had taken your advice（过去）,I should have no trouble with the work now（现在）．
2．虚拟语气在宾语从句中的用法
在动词suggest,order,demand,propose,request,mand,insist等后的宾语从句中,用虚拟语气（即Should+动词原形或只用动词原形）来表示愿望、建议、命令、请求等.在动词wish /would rather后的宾语从句中,用过去式表示与现在事实不符,用过去完成式表示与过去事实不符.如：
I suggest that we（should）set off at once．
The doctor insisted that the patient (should)be X-rayed．
I wish I were as strong as you．
would rather that you hadn”t told him．
3．虚拟语气在主语从句中的用法
在It is necessary/important/strange/natural；It is requested/suggested/desired/proposed；it is a pity等结构后的主语从句中要用虚拟语气,即Should+动词原形或只用动词原形.如：
It is necessary that he（should）be sent there at once．
It is requested that Professor Li（should）give us a speech．
It is desired that we（should）get everything ready by tonight．
4．虚拟语气在表语从句、同位语从句中的用法.
在 suggestion,proposal,idea,plan,order,advice等名词后的表语从句、同位语从句中要用虚拟语气,即should+动词原形或只用动词原形.如：
Our suggestion is that you（ should）be the first to go．
My advice is that we（should）send for Doctor Li．
Do you know the order that you（should）keep watch?
5．虚拟语气在其他状语从句中的用法
在as if引导的状语从句中,用过去式表示与现在事实不符,用过去完成式表示与过去事实不符；在so that,in order that引导的状语从句中,常用should/would/could/might+动词原形来表示虚拟语气.如：
They talked as if they had been friends for years．
She stayed at home for a few days so that she could take care of her mother．
He took a taxi to the station so that she should not miss the train．
6．虚拟语气在定语从句中的用法：
在it is time后面的定语从句中常用过去式表示虚拟
would rather do sth.”是英语中常见的一个固定惯用句式（美国英语中多用had rather）。would（或had）rather的缩写形式为 ’d rather。would (had) rather中的would并无过去的意思。该句式常用来表示选择的意愿，意谓“宁可……”、“宁愿……”、“最好……”。例如： He’d rather work in the countryside. 她宁可到农村去工作。
would rather与than连用，可构成另一个惯用句式，即：“would rather...than....”，意谓“宁可（愿）……（而）不要（愿）……”、“与其……不如……”。用以表达主语的意愿，强调经过选择后做其中一件事，而不愿做另一件事。例如： I would rather watch TV at home than go to the cinema. 我宁可在家看电视而不愿去看电影。
在使用“would rather...than...”句型时，应注意以下几点： 1. than 后边也应接动词原形，但如该句型前后连接的两个动词相同，则than之后的那个动词可省去。例如： I’d rather you know that now than afterwards. 我宁可你现在就知道这件事，而不是以后。 2. would rather...than...也可改写“would...rather than...”，其用法及含义仍不变。例如：Facing the enemies, our soldiers would die rather than surrender. 面对敌人，我们的战士宁死不屈。 3. 有时，为了表示语气上的强调，还可将rather than置于句首，例如： Rather than refuse to help you, I would borrow money from my friends. 我宁可向朋友借钱，也不愿拒绝帮助你。 4. would rather后可跟从句，表示主语宁愿让某人干某事。从句谓语动词用虚拟语气，即用一般过去时表示现在或将来要做的事；用过去完成时表示过去要做的事。如： I’d rather she set out to do the work now. 我宁愿她现在就着手做这项工作。 I’d rather you met her at the airport tomorrow morning. 但愿你明天早上能在机场见到她。 I’d rather you hadn’t told him the news that day. 我真希望你那天没有把那消息告诉他。 5. would rather后接动词的完成式，表示主语要做某事，而结果事与愿违的意思。例如： I’d rather have left a note on her desk. 我本想留张字条在她书桌上的。（事实上没有留）
b a
wish 后的从句需用虚拟语气：
该题表示同对将来情况的虚拟： wish + 主语 + would/were going to + 动词原形。因此答案是b.
第二题解释：
该题考察的是表示对将来虚拟使用的倒装的虚拟条件句，结构为：
should + 主语+v, 主语+would/should/could/might +v
上面的句式正常语序为：
if 主语+should+v, 主语+would/should/could/might +v
希望可以帮到你。