设 X_1, X_2, ..., X_n 为来自总体 N(mu_1, sigma^2) 的简单随机样本，Y_1, Y_2, ..., Y_m 为来自总体 N(mu_2, 2sigma^2) 的简单随机样本，且两样本相互独立。记 overline(X) = (1)/(n) sum_(i=1)^n X_i，overline(Y) = (1)/(m) sum_(i=1)^m Y_i，S_1^2 = (1)/(n-1) sum_(i=1)^n (X_i - overline(X))^2，S_2^2 = (1)/(m-1) sum_(i=1)^m (Y_i - overline(Y))^2，则

设 $X_1, X_2, \cdots, X_n$ 为来自总体 $N(\mu_1, \sigma^2)$ 的简单随机样本，$Y_1, Y_2, \cdots, Y_m$ 为来自总体 $N(\mu_2, 2\sigma^2)$ 的简单随机样本，且两样本相互独立。记 $\overline{X} = \frac{1}{n} \sum_{i=1}^n X_i$，$\overline{Y} = \frac{1}{m} \sum_{i=1}^m Y_i$，$S_1^2 = \frac{1}{n-1} \sum_{i=1}^n (X_i - \overline{X})^2$，$S_2^2 = \frac{1}{m-1} \sum_{i=1}^m (Y_i - \overline{Y})^2$，则

• A. $\frac{S_1^2}{S_2^2} \sim F(n, m)$.
• B. $\frac{S_1^2}{S_2^2} \sim F(n-1, m-1)$.
• C. $\frac{2S_1^2}{S_2^2} \sim F(n, m)$.
• D. $\frac{2S_1^2}{S_2^2} \sim F(n-1, m-1)$.