A. $N(2,\frac{4}{50})$
B. $N(\frac{2}{50},4)$
C. $x^{2}(50)$
D. $x^{2}(49)$
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设X_(1),X_(2),...,X_(n)是来自总体X的样本，则(1)/(n-1)sum_(i=1)^n(X_(i)-overline(X))^2是（）A.
设X_(1),X_(2),...,X_(n)为总体X的简单样本，则样本均值overline(X)=(1)/(n)sum_(i=1)^nX_(i).A. 对B.
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