... as if/as though ...
结构︰…as if/as though…现在式/过去式/过去完成式
说明︰此句型意为“彷佛…;好像…一样”。as if，as though 是<副词><连接词>，引导<副词子句>。<子句>中，可用现在式，以表示事实;也可用过去式或<过去完成式>，分别表示与现在或过去事实相反的<假设语气>。
He speaks like that as if he doesn’t want to attend the meeting.他那样说话，似乎不想参加会议。
He walks as if he is drunk. 他走起路来好像他真的醉了。
He felt as if he almost wished to kill them. 他感觉彷佛几乎要杀掉他们。
The baby opened the book as if he were able to read. 这个婴儿打开书本彷佛他会念书。
The nurse attends on the patient as if he were her father.
这护士照顾这位病人彷佛在照顾她爸爸似的。
He ran into the room as if he had seen something terrible.
他跑进屋子，彷佛他看到什么可怕的东西。
She looks as if nothing had happened to her. 她当时看起来好像什么事都没发生似的。
It seems/looks as if ...
结构︰It seems/looks as if…
说明︰此句型意为“似乎…”。本句型中的 as if <子句>可用以表示事实，或<假设语气>。
It looks as if it is going to rain. 好像要下雨了。
It seems as if he knows everything. 他似乎是个万事通。
It seems as if he knew everything, but in reality, he is as stupid as can be.
他似乎是个万事通。其实他是再愚蠢不过了。
It looks as if she had just come back from outer space.
她看起来彷佛刚从外层空间回来似的。
It seemed as if he had finished the work. 他似乎已经完成了这个工作。
It seemed as if he would never finish the work. 他似乎永远完成不了这个工作。
If it were not for ...
结构︰if it were not for+名词/子句，主词+would/should 等+原形动词…
说明︰此句型意为“若非(有)…”。此类句构专门用于表示与现在事实相反的<假设语气>。亦可用“but for+<名词>”或“without+<名词>”代替。were 可以提前，省略 if，如例句3。
If it were not for his presence, I would punish you. 要不是他在场，我会处罚你的。
But for your advice, I should have failed. 要不是你的忠告，我会失败的。
But for music (=Were it not for music), life would be dull. 要不是音乐，人生会很无聊。
If it were not for oxygen and nitrogen in the air, no man could live on the earth.
大气中如果没有氧和氮，人就无法生存于地球了。
Without air, all living things would die. 若非空气，所有的生物都会死亡。
Without newspaper, we would get behind the times. 要不是报纸，我们都赶不上时代了。
I should be lonely, were it not for the birds and the flowers. 我会寂寞，若非有鸟也有花。
Were it not for his help, I could not finish the work.若非有他的帮助，我就不能完成这件工作。
Were it not for science, we could not live a comfortable live.
若非科学，我们无法过着舒适的生活。考试大－全国最大教育类网站(www．Examda。com)
If it had not been for ...
结构︰if it had not been for+名词/子句，主词+would/should 等+原形动词…
说明︰此句型意为“若非(有)…”。此类句构专门用于表示与过去事实相反的<假设语气>。
If it had not been for his help, I should have failed. 如果没有他的帮忙，我应该已经失败。
Had it not been for your timely help, our company would have been on the verge of bankruptcy. 若非你及时伸出援助之手，本公司将会濒临破产的边缘。
If it had not been for these experiments, the improvement of the machine would have been impossible. 要不是这些实验，这部机器也许就不可能改良了。
Had it not been for the kind guide, I might have got lost in the mountains.
要不是这位好心的向导，我可能就在山中迷路了。
If it had not been that he was here, I would have punished you.
要不是他在场，我当时就会处罚你。
I demand/insist that ...
结构︰主词1+意志动词(demand/insist 等)+(that)+主词2+(should)+原形动词
说明︰意志<动词>有四类：建议(suggest，recommend，propose，advise，urge 等)，要求(desire， ask，demand，require，request，maintain，insist 等)，命令(order，command 等)，规定( rule，regulate，stipulate 等)。其后接 that-<子句>时，该<子句>里的<动词>要用原形或“should+<动词>”。美式英语通常省略 should。
The committee moved that the meeting (should) be adjourned. 委员提议休会。
His parents demanded that he (should) be back by ten. 他的父母要求他十点以前回家。
The employees demand that their salaries be raised. 员工们要求加薪。
They ruled that the law (should) not be imposed. 他们规定不应加重法律。
His father ordered that he (should) keep a diary in English.
他的父亲规定他要用英文写日记。
My mother encouraged me and insisted that I continue my education.
我妈妈鼓励我，而且坚持我应该继续我的教育。
He insisted that I (should) apologize to her. 他坚持我应该向她道歉。
Recently, many states have insisted that high schools teach students how to drive.
最近，许多州坚持中学应该教学生如何开车。
His father insisted that they (should) move to the country. 他爸爸坚持他们应该搬到乡下。
责任编辑：八月骄阳
