有一句子：It hasbecome as common in colleges and universities for students to grade teachers as for teachers to grade students.
it是句子的形式主语吧？那么真的的主语是是从for开始还是从第一个to开始到结尾？还有就是连个as的用法有些不明白。请指教我..谢谢！！
在大学里，学生们给教师评分已经象教师们给学生评分一样普遍了。这句话是同级比较的句子， A is as 形容词 as B对号入座，谁是A，就是主语，it是形式主语。或者这么看： it is common for students to grade teachers.主语是不定式，for 引导逻辑主语students
