设总体,…,是来自总体的一个样本,则的无偏估计量是( ).

A、<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/154563383291750cd2dda01544deabc48386b77a484b8image42.png">

B、<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/1545633833006f14b3285c1d54526a559a705fdf03ca1image43.png">

C、<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/1545633833104e36178594dea45c983622dddeb8f0cf0image44.png">

D、<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/15456338331905078883a1e454fad8c32c131fac86679image45.png">