12. 統計量 z = √n(x - μ) / σ的標準差為？ (A) 0 (B) 1 (C) ? (D) ?

13. 又\( \hat{\theta}_1 \) 和 \( \hat{\theta}_2 \)同樣為參數θ的點估計值(Point estimator)，下列何者符合估計值\( \hat{\theta}_2: \)具備一致性(Consistency)的敘述？(A) \( \text{E}[\hat{\theta}_2] = \theta \) (B) \( \text{Var}(\hat{\theta}_1) < \text{Var}(\hat{\theta}_2) \) (C)\( \lim_{n \to \infty} \text{Var}(\hat{\theta}_2) = 0 \) (D)\( \text{E}[\hat{\theta}_2] = 0 \)