A、<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/1545530039805a227c7f407754147a342199151d66b71image78.png">不是<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/154553003988791a0b68b05704781a3d739d229b6bb2cimage79.png">的无偏估计;
B、<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/1545530039978a2e6e735a86b49399a5f36e7d6365614image80.png">不是<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/1545530040078f7ecf8cc2b354f3db6fcbff5cf26d00aimage81.png">的无偏估计;
C、<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/154553004016774dfa6d9eba14860a3fa33012f7eba71image82.png">作为<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/15455300402616d6ced38f34c40f980f3eee59a490772image81.png">的无偏估计比<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/154553004034875b3e4f1dd7940eb834331c0c4f21b17image83.png">更有效;
D、<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/15455300404459a4ca39fac84468a9090aac8859ae1a0image83.png">作为<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/1545530040552f4c0f1acad4a4941a274186c67154527image81.png">的无偏估计比<img src="https://s3.cn-north-1.amazonaws.com.cn/qingshuxuetang/examination/imgUplod/15455300406335852c455228145f2b3710c506a2a5276image82.png">更有效.
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具有
和
,
是
的样本,则下列正确的是( )
