(B) (hat {sigma )}^2=dfrac (1)(n)sum _(i=1)^n(({X)_(i)-overline (X))}^2.-|||-(C ({sigma )_(sigma )}^2=dfrac (1)(n-1)sum _(i=1)^n(({X)_(i)-mu )}^2. (D) (overrightarrow {sigma )}^2=dfrac (1)(n)sum _(i=1)^n(({X)_(i)-mu )}^2.

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