Many people consider it _________, from which a lot of children benefit.

A．a worth doing cause

B．a cause worth to do

C．a worthwhile cause

D．a worthless cause

一次考试中7名学生的成绩（单位：分）如下：61，62，71，78，85，85，92，这7名学生的极差是     分，众数是    分。