理工类辅导资料：句型分析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。
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.