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【单选题】
设总体 的数学期望和方差分别为 , 为来自总体 的一个样本, 为样本均值, 为2阶中心矩, 为顺序统计量,则下列统计量是参数 的无偏估计量的是( ).A.
;
B.
;
C.
;
D.
.
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【简答题】A．They spend too much time on sports. B．They are always watching TV programs. C．They like to play s on TV. D．They take little interest in their wives.
【简答题】属于国家二级保护野生药材物种的是 查看材料
【简答题】A．Because they lack self-discipline in their studies. B．Because they spend too much time on the Internet. C．Because they have not exerted their utmost. D．Because they have developed poor relationships...
【简答题】A．Because they lack self-discipline in their studies. B．Because they spend too much time on the Internet. C．Because they have not exerted their utmost. D．Because they have developed poor relationships...
【单选题】边长为a的立方框架上，沿对角线AB作用一力，其大小为P;沿CD边作用另一力，其大小为1.732P/3，此力系向O点简化的主矩大小为()。
A.
2.449Pa
B.
1.732Pa
C.
2.449Pa/6
D.
1.732Pa/3
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