设 $X_1, X_2, \cdots, X_n, \cdots$ 为独立同分布的随机变量序列, 且均服从参数为 $\lambda(\lambda>1)$的指数分布, 记 $\Phi(x)$ 为标准正态分布函数, 则
$\text{A.}$ $\lim _{n \rightarrow \infty} P\left\{\frac{\sum_{i=1}^n X_i-n \lambda}{\lambda \sqrt{n}} \leqslant x\right\}=\Phi(x)$.
$\text{B.}$ $\lim _{n \rightarrow \infty} P\left\{\frac{\sum_{i=1}^n X_i-n \lambda}{\sqrt{n \lambda}} \leqslant x\right\}=\Phi(x)$.
$\text{C.}$ $\lim _{n \rightarrow \infty} P\left\{\frac{\lambda \sum_{i=1}^n X_i-n}{\sqrt{n}} \leqslant x\right\}=\Phi(x)$.
$\text{D.}$ $\lim _{n \rightarrow \infty} P\left\{\frac{\sum_{i=1}^n X_i-\lambda}{\sqrt{n} \lambda} \leqslant x\right\}=\Phi(x)$.