①Why John was late for the class has been unexplained.状语

　　②Which part of the country he will travel to needs discussing.定语

　　③Where cars will be parked in the future is a question.状语

　　④What we should do next remains unknown.宾语

　　⑤Whoever is interested in the activity can sign your names.主语

语法点三 主语从句中用it作形式主语的结构 　　1.It＋be＋形容词(obvious, true, natural, strange, etc.)＋主语从句

　　It is doubtful whether she will be able to come to the party.

　　她是否能来参加聚会还很难说。

　　It is necessary that a college student (should) master one or two foreign languages.

　　大学生掌握一两门外语是必要的。

　　[点津]　在"It＋ be＋形容词＋主语从句"结构中，若形容词为important/necessary/

　　strange等时，主语从句中的谓语用"(should) do"。

　　2．It ＋ be＋名词词组(no wonder, an honour, a pity, a/no surprise, etc.)＋主语从句

　　It's a pity that you missed the film.

　　你没有看那部电影真是太遗憾了。

　　3．It ＋be＋过去分词(said, reported, thought, expected, proved, etc.)＋主语从句

　　It is reported that no passengers were injured in the accident.

　　据报道在这起事故中没有乘客受伤。

　　[点津]　在"It ＋ be＋过去分词＋主语从句"结构中，过去分词若为suggested/ordered/

　　required/advised等时，主语从句中的谓语用"(should) do"。

　　4．It＋不及物动词(happen, seem, appear, etc.)＋主语从句

　　It happened that I was out that day.

　　碰巧那天我不在。

　　5．It ＋ 及物动词＋宾语＋主语从句

　　It surprised him why they came to visit him suddenly.

　　让他吃惊的是他们为什么突然都来看他。

　　即时演练3

　　句型转换

　　①That he suddenly fell ill last month surprised us.

　　→It surprised us that he suddenly fell ill last month.

　　②Whether she will come or not doesn't matter.

→It doesn't matter whether she will come or not.