常见的it开头的句型有 it is … that … 强调句型，也有it充当形式主语的句型，在这两种句型中，不少华慧考博的学员分不清什么是强调句型，什么时候it充当形式主语。
华慧考博：it 开头的特殊句型有哪些？
我们先来梳理一下it引导的形式主语句型有哪些： 动词不定式，动名词或主语从句作主语时，通常用it作形式主语，放到句首，而真正的主语放在句尾，常见句型有如下： 1. It + be + 形容词+主语从句，如： It is uncertain whether he can come to Jenny’s birthday party or not. 2. It + be + 名词词组 + 主语从句，这类名词有：a fact, a pity, a shame, an honor，a question等，如： It’s a pity that you missed the exciting football match. It remains a question whether he will come or not. 3. It + be + 过去分词 + 主语从句，这类过去分词有：announced, believed, expected, hoped, decided, reported, said, shown等， 如： It is reported that 16 people were killed in the earthquake. It is not decided who will give the operation to the patient. 4. It + 不及物动词(seem, appear, happen等) + 主语从句, 这类不及物动词有：appear, happen, seem等， 如： It seemed that he didn’t tell the truth. It happened that I was out when he called. 5. It + be + 形容词 + for sb.）+ 动词不定式 这类句型常用形容词easy, difficult, hard, important, possible，wise等作表语，有时候为了强调不定式动作的执行者，常在不定式前加for sb，如： It’s necessary for the young to master two foreign language. It is unwise to give the children whatever they want. 这类形容词有：easy, difficult, hard, important, possible，wise 6. It + be + 形容词 + of sb. + 动词不定式，这类形容词常是表示心理品质,性格特征的形容词，如：kind, nice stupid, clever, foolish, polite, impolite, silly, selfish, considerate等。某人和这些形容词可以构成主系表结构。如： It’s very kind of you to help me with the work. =You are kind to help me. It seemed selfish of him not to share his dictionary with others. =He seemed selfish not to share his dictionary with others. 7. It + be +名词词组 + 动词不定式，如： It is not a good habit to stay up too late. 8. It + be + 名词或形容词 + 动名词，这类名词和形容词常常是：good, no good, no use, a waste of, useless, senseless等，如： It’s a waste of time talking to her any more. It is no use arguing about the matter with him. 9. It + take ( sb. )+ 时间（金钱）+ 动词不定式，如： It took the workers almost three years to finish building the dam. It will take a whole day to get to the top of the mountain on foot.
而 it引导的强调句型结构为：It is + 被强调部分+ that … 该句型是强调句型，将被强调的部分放在前面，其他部分置于that之后。被强调部分可以是主语，宾语，表语或状语。如果把那种句型结构划掉后，应该是一个完整无缺的句子。这也是判断强调句型与其他从句的方法。 It was about 600 years ago that the first clock with a face and an hour hand was made. It was they that cleaned the classroom yesterday.
另外一个it引导的特殊句型为 it is not until + 被强调部分+ that … 该句型主要用于强调时间状语，译成汉语“直到…才…”，可以理解为 not … until 的强调形式： It was not until she took off her glasses that I realized that she was a famous film star. = Not until she took off her dark glasses did I realize she was a famous film star. = Ididn’t realize she was a famous film star until she took off her glasses.
