概率方差D(X)公式简介：The little girl has never seen her mother be so cruel to her, so she tried her best to hold back and prevent herself from crying, but her shaking body showed that the little girl was enduring it very hard.
The little girl has never seen her mother be so cruel to her, so she tried her best to hold back and prevent herself from crying, but her shaking body showed that the little girl was enduring it very hard.
