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it用作形式主語(yǔ)的用法

一、基本用法

當(dāng)不定式、動(dòng)名詞、從句等用作主語(yǔ)時(shí)，避免頭重腳輕，通常在句首使用形式主語(yǔ)it，而把真正的主語(yǔ)放在句子末尾：

Is it necessary to tell his father everything? 有必要把這一切都告訴他父親嗎?

It’s no good sitting up too late. 熬夜沒(méi)有好處。

It is quite clear that he has read the book. 很顯然，他讀過(guò)這本書。

It doesn’t matter what he says. 他說(shuō)什么沒(méi)關(guān)系。

二、幾種特殊的形式主語(yǔ)

(1) 用作動(dòng)詞look, seem, appear, happen, occur, follow等的主語(yǔ)(后接that從句或as if從句)：

It seems as if it is going to rain. 看來(lái)要下雨了。

It seems that he knows everything. 他好像什么都知道。

It (so) happened that I had no money with me. 碰巧我沒(méi)帶錢。

From this witness it follows that he must be guilty. 根據(jù)該證人的證詞判斷，他一定有罪。

(2) 當(dāng)系表結(jié)構(gòu)后接有if 或when引出的狀語(yǔ)從句時(shí)，通常在系表結(jié)構(gòu)前使用形式主語(yǔ)表示說(shuō)話人對(duì)某情況的看法： (from www.52ysedu.com)

It was a great surprise to me when he did a thing like that. 他這樣做使我很吃驚。

It would be a tragedy if anything went wrong. 如果出了什么事就是一個(gè)悲劇。

(3) 用于其他固定句型，如if it were not for…(若不是因?yàn)?/FONT>)，it’s time that…(該…了)等。