it 用作形式主語可以代替哪些成分

it用作形式主語時可代替不定式、動名詞、從句等。一般說來，當不定式、動名詞、從句等復雜成分用作句子主語時，為保持句子平衡，通常把真正的主語放在句末，而在句首使用形式主語it。

1. 代替不定式

It is difficult to make crossing over a sea. 橫渡大海是件難事。

It is very easy to deal with Australians. 與澳大利亞人打交道容易。

It is dangerous to bathe in the sea here. 在這兒的海里游泳是危險的。

It is her custom to go for a walk on Saturday morning. 她慣常在星期六早上出去散步。

It is difficult to breathe at these altitudes. 在這些高的地方人們會感到呼吸困難。

It is pleasant to walk among the trees in the evening. 晚上在樹林中走一走令人心曠神怡。

It is advisable always to wear a safety belt when you’re driving. 開車的時候最好總是系著安全帶。

2. 代替動名詞

It is nice visiting new places. 到陌生地方去玩真是有意思。

It is man’s social being that determines his thinking. 人的社會存在決定人的思想。

It is a bore having to go out again on a cold night like this. 像今天這樣的夜晚還得出門真煩死人。

3. 代替從句

It is appropriate that he (should) be present. 他應到場才對。

It is astonishing to me that he should be absent. 他竟未出席令我驚訝。

It is well known that Edison invented the electric bulb. 眾所周知，是愛迪生發明了燈泡。

It is desired that this rule should be brought to the attention of the staff. 希望這條規則引起全體職員的注意。

It is a question that needs very careful consideration. 這是一個需要仔細考慮的問題。(G31)

It was astonishing to everybody that the court had made such a decision. 法庭作出這樣的判決，所有人都感到很驚訝。

It is amazing that she should have said nothing about the murder. 令人驚奇的是她對這樁兇殺案竟然不置一詞。