单项选择题

设X服从正态分布,E(x)=-1,E(X2)=4,取样本X1,X2,…,Xn则均值~(    )
   A.    B.
   C.    D.

A.174.24.96:6088/Latex/latex.action?latex=XGJhcntYfQ%3D%3D'
B.C.174.24.96:6088/Latex/latex.action?latex=TlxsZWZ0KCAtXGZyYWN7MX17bn3vvIxcZnJhY3sxfXtufSBccmlnaHQp'
D.E.174.24.96:6088/Latex/latex.action?latex=TlxsZWZ0KCAtMe%2B8jFxmcmFjezN9e259IFxyaWdodCk%3D'
F.G.174.24.96:6088/Latex/latex.action?latex=TlxsZWZ0KCAtXGZyYWN7MX17bn3vvIw0IFxyaWdodCk%3D'
H.I.174.24.96:6088/Latex/latex.action?latex=TlxsZWZ0KCAtMe%2B8jFxmcmFjezR9ezR9XHJpZ2h0KQ%3D%3D'