欲描述20个血清滴度资料的集中趋势，最好采用（）
A.均数
B.众数
C.中位数
D.几何均数与中位数
E.几何均数
参考答案：E
Sam ______ coins since he was eleven years old, and now he has hundreds of them.
A．collected
B．had collected
C．has been collecting
D．had been collecting
按目前某市的护士数与床位数之比，是规划数的( )。
A．50%
B．138.9%
C．72%
D．172%
