英语中it在句中可以充当形式主语，后面接that引导的从句为真正的主语。这种用法的目的是为了句子的平衡将真正的主语移到后面而避免句子结构的头重脚轻
it作形式主语的常见句型：
(1)It is+adj.+主语从句(用于此句型的形容词有：easy,hard,difficultpossible, important,impossible,neceseerybad.interesting,surprising等)(2)It is+n.十主语从句(用于此句型中的词汇有：a pity,a shame,no wonder ones duty,fun,good manners,bad manners等)
(3)It is+及物动词的过去分词+that从句(此句型中常见的及物动词的过去分词有：said，told, known, reported, thought,believed, considered等)
(4)It十不及物动词+主语从句(此句型中常见的不及物动词有：seem，appear，the happen等）
①It is evident that the local government is trying tohelp the graduates with employment.省很明显，当地政府正试图帮助大学生就业。
②Its a pity that the research indicates that 81% of teachers are dissatisfied with their salary.遗憾的是，研究表明81%的教师对他们的薪水不满意。
③Its said that he is doing well in school.据说他在学校里表现很好。
④It seems that he is not willing to go there.看来他不愿意去那里。
【多维练透】
补全句子
① It is obvious to the students (对学生来说很明显)that they should get well prepared for their future.
②It is a pity that (真遗憾) Jane and George can make it to the party.
③It is important that (很重要) everyone should learn to get along well with others in a new environment.
④.But it was evident that ideas were changing in the 13thcentury when painters like Giotto di Bondone began to paint religious scenes in a more realistic style.(教材P.)但是很显然，到了13世纪时，(人们的)观念发生了变化，像乔托这样的画家开始以一种比较现实的风格来描绘宗教场景。
