1. It is/ was obvious/ clear/ true/ possible/ certain...that...

......是明显/清楚/真的/可能/肯定的。

　　这是主语从句最常见的一种结构。句中it作先行词，代替名词性从句。该结构中的名词性从句可用that, what, when等引导。

It is obvious that she is very clever.

很明显，她挺聪明的。

It is not certain what caused the accident.

还不肯定那个事故是什么引起的。

It isn't remotely possible that you will be chosen to go.gkstkgkstkgkstk]

挑选你去的可能性并非很小.。

　　it作形式主语代替从句的句型还有：

① It is+n.+that-clause

② It is+过去分词+that-clause

③ It is+ vi.+that-clause

It's natural that teachers are strict with their students.gkstkgkstkgkstkgkstk]

老师对学生要求严格是很自然的事。

It's obvious that this destruction will become more dangerous in the future. 【一讲一练】

单项选择。

1. It has been proved _____ eating vegetables in childhood help stop protecting you against serious illness in later life.

A. if B. because

C. when D. that

2. It is by no means clear _____ the president can do to end the strike.

A. how B. which

C. that D. what

【答案】

1. D 2.D

【解析】

1. 句子为主语从句，it是形式主语。句意：实践证明小时候多吃蔬菜有助于在后来的生活中帮助你抵抗疾病。

2. 考查名词性从句的引导词。句中it是形式主语，空后的从句为真正的主语;主语从句中缺少do的宾语，故选择what 作为主语从句的引导词且充当从句中谓语动词do的宾语。