题目

一个容量为40的样本，数据依次为x1,x2,…,x40,若这个样本的标准差为s=,记.则等于(    ) A.2                                       B.C.                                   D.4 答案：AThe new supermarket was once close to closing down. But since the underground was opened, business has been _______.A. picking up B. coming upC. making up D. turning up