（1）介词或介词短语，如but for, but that, without, in case of, under more favorable condition等。
the leadership of the party, we could not be living a happy today.=If there hadn't been the leadership of the party, we could not be living a happy today.
A. In spite of B. But for C. Because of D. As for 答案选B。
But that she was afraid, she would have said no.
（2）连词，如：so that, unless, in case, supposing, lest, provided（倘若……），for fear that（唯恐），in order that, on condition that, if only（要是……就好了）等。
She listened carefully in order that she might discover exactly what he wanted.=if she listened carefully ,she might discover exactly what he wanted.
If only I had more money, I could buy a car.
（注：lest, for fear that 和 in case 引起的从句中谓语动词多用should+动词原形，但可以不用虚拟语气，而用动词的陈述语气形式。）例如：
The foreign teacher spoke slowly in case we misunderstood him. 这位外籍教师说得很慢以免我们听不懂。
Care must be taken in using this method lest overflow should occur.在使用此法时要小心谨慎，以免会发生溢流现象。
（3）通过上下文及内在含义，句中往往有but, otherwise, unfortunately等类似转折词。
I thought the children when we returned home, but they were still awake.
A. were sleeping B. would be sleeping C. had been sleeping D. would sleep选择 B。
A more careful person would not have made so many mistakes.
A less conscientious man wouldn't have tried so hard to get this job done.
Having known in time, we might have prevented the accident.
Born ten days earlier, the boy could have seen his late father.
（6）动词不定式短语。一般intended/meant/hoped/wished/planned 或 was/were+不定式完成式或had intended/meant/planned/hoped/wished/+不定式一般式表示虚拟。
I intended I should call on you, but I was busy at that time.
To hear him speak French, you would take him for an Englishman.
She would be stupid not to accept his invitation.
It would be easier to do it this way.
A judicious man would not have committed suicide.
A diligent student would have worked harder.
All things considered, the price would be reasonable.
Anyone who had been in your position would have done the same.
A nation, which stopped working, would be dead in a fortnight.
I should have called to make an airline reservation, but I didn't.
The porter ought to have called the fire-brigade as soon as he saw the fire in the stock, which went up in smoke.
God bless you!
All magnets behave the same, be they large or small.
She'll be sixteen years odd, com May.（come May =when May come）。
If that be so, we shall take action at once.