3. 用在以下主语从句中
用在一些与表示要求、建议、命令等动词意义相似的形容词所带的主语从句中。这时谓语动词也用”should +动词原形”或省略should, 只用动词原形。 这些形容词有：
advisable, desirable, essential, important, impossible, necessary, possible, strange, urgent, incredible (难以置信的), natural, insistent, preferable, crucial (关键的), vital(至关重要的)以及desired, decided, recommended, suggested, deserved, etc. 例如：
1) It is necessary that the machines (should ) be oiled(给…上油) every day.
2) It is important that the students (should) take part in the social practice.
3) It is desired that all the students (should) pass the final examination.
4) It is required that all the committee members (should) be present.
5) It has been decided that the meeting (should) be postponed (推迟) till next week.
4. 用在某些名词后的表语从句或同位语从句中
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这时谓语动词用“should +动词原形”或省略should， 只用动词原形。 这些名词有：
suggestion, proposal, advice, decision, desire, order, idea,
motion(动议，提议), recommendation, request, requirement, resolution, etc. 例如：
1) Our suggestion was that such device (should) be designed and produced without delay.
2) His desire is that he (should) visit the Great Wall of China someday.
3) We all agree his proposal that we (should) go go see the exhibition.
5．用在动词wish 后面的宾语从句中
虚拟语气用在动词wish 后面的宾语从句中，表示一种与实际情况相反的愿望。
5.1 与现在事实相反，wish后用动词的过去式 例如:
1) I wish I knew how to operate the computer. 2) I wish you were more careful.
5.2 与过去事实相反，wish 后用过去完成时或 “could +现在
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完成时” 例如：4
1) I wish you had come to our New Year’s Party. 2) She wishes that she could have been there yesterday. 5.3 与将来相反，wish后用（would/could+动词原形） 例如：
1) We wish that you could come and join us. 2) I wish it would stop raining tonight.
注：动词wish 如果是过去式，后面宾语从句中的虚拟语气形式不变。 例如：
1) She wished she knew how to drive a car.
2) I wished I hadn’t been so forgetful. Then I shouldn’t have missed the talk.
6．虚拟语气用在if only引起的从句及感叹句中
通常后面用过去式或过去完成时，与wish后面的谓语动词用法相同。常译成“要是…就好了”， “但愿…”，通常表达强烈的愿望或遗憾。 例如：
1) If only o9 could help you! 2) If only the wind would stop!
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3) If only I were ten years younger! 4) If only he had not left!
7. 用在由as if 或as though 引导的状语从句中 谓语动词形式与wish后面的谓语动词用法相同。 例如：
1) They talked as if they had been friends for years.
2) My mother looked after the orphan as if he were her own child.
8. 用在以lest, for fear that 引导的从句中
这时谓语动词多用 “should +动词原形”， 也可省略should. 例如：
1) He took his raincoat with him lest it (should) rain.
2) She put the coat over the child for fear that he (should) catch cold.
9．用在“It’s (about/high) time”句型中(意为：是该做…的时候了。) 例如：
1) It’s time we left.
2) It’s high time we went to bed.
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