If 主语＋过去时，主语＋should(could, would, 或might)＋动词原形，如：
If I were you, I would study hard.
If it rained, I would not be here now.
If 主语＋had＋过去分词，主语＋should(could, would, 或might)＋have＋过去分词，如：
If the doctor had come last night, the boy would have saved.
If I had not studied hard, I would have failed in the exam last term.
If 主语+should(were to, 过去时)＋do，主语＋should(could...)＋原形do，如：
If it should rain tomorrow, we would stay at home.
If I were to go to the moon one day, I could see it with my own eyes.
If you missed the film to night, you would feel sorry.
3、在条件句中如果出现were, had, should可省去if，将主语与这些词倒装，例如：
Had the doctor come last night, the boy would have saved.
Were I to go to the moon one day, I would see it with my own eyes.
Should it rain tomorrow, we would stay at home.
在表示命令、建议要求、惊叹时的名词性从句中需用虚拟语气，基本句型：主语＋(should)＋动词原形，如：Mother insisted that John go to bed at 9 o"clock.（宾语从句）
We suggested that the meeting should not be held.
It was required that the crops should be harvested at once.（主语从句）
The suggestion that he be invited was rejected.（同位语从句）
That is their demand that their wages be increased.（表语从句）
与现在愿望不一致——主语＋过去时：I wish I were you.
与过去愿望不一致——主语＋had＋过去分词：I wish I had visited the white House when I was in the states.
与未来愿望不一致——主语＋would(could)＋原形：I wish I could meet you tomorrow at the party.
It"s time that you went to school. 或It"s time that you should go to school.
3、If only引起的感叹句相当于“How I wish＋宾语从句”：
If only he could come! 他要能来就好了。
If only I had known the answer! 我要早知答案就好了。
4、would rather, as if(though)引导的句子也需使用虚拟，表示过去的情况用过去完成时，表示现在与将来的情况用过去时，如：
I"d rather you posted the letter right away.
I"d rather you had returned the book yesterday.
She loves the children as if they were hers.
Alan talked about Rome as if he had been there.
5、without, but, but for, otherwise引起的短语或句子常暗含着含蓄条件：
Without you, I would never know him.
But for your cooperation, we wouldn"t have done the work so well. = If it were not for your cooperation, we wouldn"t have done the work so well.
（注：without / but for... = If it was not for.../ If it hadn"t been for...）
But that she was afraid, she would have said no.
I would be most glad to help you, but I" am busy now.
I am busy now; otherwise I would do you the favor!
1、It is important that a college student ______ a foreign language.
A．will master B．master C．masters D．would master
2、It is strange that she ______ without saying a word.
A．should have gone out B．went C．should go out D．goes out
3、If my lawyer ______ here last Saturday, he ______ me from going.
A．had been, would have prevented B．had been, would prevent C．were, would prevent D．were, would have prevent
4、 ——“He is a brave man.”
——“Yes, I wish I ______ his courage.”
A．have B．had C．will have D．may have
5、If it ______ rain, the crops would be saved.
A．should B．will C．is going to D．was to
6、He ordered that the medicine ______ by a special plane.
A．was sent B．would be sent C．should send D．be sent
7、If you ______ the medicine, you ______ better now.
A．took, would feel B．had taken, felt C．had taken, would feel D．took, would have felt
8、She is my sister, but she often acts as if ______ my mother.
A．is B．was C．were D．had been
9、I went to bed early last night, but I wish I ______ so.
A．didn’t do B．hadn’t done C．haven’t done D．couldn’t do
10、I’d rather he ______ tomorrow afternoon.
A．will come B．comes C．coming D．came
1、B 2、A 3、A 4、B 5、A 6、D 7、C 8、C 9、B 10、D