设总体<img src="/lqwvjeImg/6f/6f187dc7103766cde28289eaf52a92cc.png"style="width:18px;height:17px;">具有<img src="/lqwvjeImg/4e/4e42daedc7d92f2f74e70d87d40fbf77.png"style="width:69px;height:21px;">和<img src="/lqwvjeImg/a4/a46d9b1b75711590c90f6222d27a7785.png"style="width:42px;height:21px;">,<img src="/lqwvjeImg/50/50d6ec6e916c3ab8016d15e175c5beaa.png"style="width:89px;height:24px;">是<img src="/lqwvjeImg/6f/6f187dc7103766cde28289eaf52a92cc.png"style="width:18px;height:17px;">的样本,则下列正确的是( )<br>·<img src="/lqwvjeImg/dd/ddeabf6bf907d428bf23141962df8740.png"style="width:102px;height:24px;">不是<img src="/lqwvjeImg/80/809397aeee96f6dbc8813ef60a64f0d7.png"style="width:16px;height:17px;">的无偏估计;<br>· <img src="/lqwvjeImg/6a/6ad3cb57c74c50554a725bef77094807.png"style="width:86px;height:45px;">不是<img src="/lqwvjeImg/89/89643c1073895fa982b8576e95074861.png"style="width:13px;height:14px;">的无偏估计;<br>·<img src="/lqwvjeImg/0d/0dfc750dc87e89933cba3f251e98fabe.png"style="width:18px;height:21px;">作为<img src="/lqwvjeImg/89/89643c1073895fa982b8576e95074861.png"style="width:13px;height:14px;">的无偏估计比<img src="/lqwvjeImg/bf/bf0cff44ecced13ba0d6723b9ad85691.png"style="width:21px;height:24px;">更有效;<br>· <img src="/lqwvjeImg/bf/bf0cff44ecced13ba0d6723b9ad85691.png"style="width:21px;height:24px;">作为<img src="/lqwvjeImg/89/89643c1073895fa982b8576e95074861.png"style="width:13px;height:14px;">的无偏估计比<img src="/lqwvjeImg/0d/0dfc750dc87e89933cba3f251e98fabe.png"style="width:18px;height:21px;">更有效.