阅读下面两幅图，完成下列各题。

摩擦力对我们有时是____，有时是____。

把下面的图片与所给的描述对号入座。
A        B          C 
D                E
____ He is of medium height and build, with two small eyes. He is a pop singer. And he likes playing basketball very much. He is very popular with young people.
____ He is short and of medium build. He has short black hair. He is a funny actor.
____ She is heavy. She has short brown hair. She always wears glasses. She sings very well.
____ He is very tall and has short black hair. He is a basketball player, and he plays it very well. Now he is a college student in Shanghai Jiaotong University.
____ She is thin, with long black hair and big eyes. She is a movie star. She is in the play "Palace", and she is very popular with young people.