问题补充：
It is important students carefully in class .
A. for, listening.
B. of , listen
C. for, to listen
D. of , to listen.
答案：
A. for, listening.
B. of , listen
(答案→)C. for, to listen
D. of , to listen.
解析：
试题分析:强调句式， It is adj for sb to do sth，做某事对某人来说怎么样。本句中it是形式主语，指代后面不定式内容做形式主语.句意:对于学生们来说,上课认真听讲很重要.结合语境可知选C.
