题目

下列函数中，可作为某一随机变量的分布函数的是 $\underline{\qquad}$.

A. $F\left(x\right) = \frac{1}{1 + {x}^{2}}$
B. $F\left(x\right) = \frac{1}{\pi }\arctan x + \frac{1}{2}$
C. $F\left(x\right) = \left\{ \begin{array}{ll} \frac{1}{2}\left({1 - {\mathrm{e}}^{-x}}\right), & x > 0, \\ 0, & x \leq 0 \end{array}\right.$
D. $F\left(x\right) = {\int }_{-\infty }^{x}f\left(t\right) {dt}$,且 ${\int }_{-\infty }^{+\infty }f\left(t\right) {dt} = 1$