I felt so hungry at midnight, but I couldn't find ________ to eat in my flat.[ ]

A) everything

B) something

C) anything

D) nothing

已知X₁，X₂，…，X_n是来自正态总体N(0，σ²)容量为n(n＞1)的简单随机样本，样本均值与方差分别为

试求统计量

的期望

与方差