题目2单选题
重复n次测量模具的重量的权w1,w2,……wn,其标准差的无偏估计为A. <img src="https://tihai-oss-cloud.itihey.com/img/2f8d7cbf108cd03819ebef646057e2b5.png">B. <img src="https://tihai-oss-cloud.itihey.com/img/e735f699cef797b0567d816ddbd9da3f.png">C. <img src="https://tihai-oss-cloud.itihey.com/img/41aa79f0584c7df4a5a6836350ef5280.png">D. <img src="https://tihai-oss-cloud.itihey.com/img/8a1e1e1a21a6c178de65b71e26000cab.png">