设 $f(x)$ 是 $[0,1]$ 上单调增加的连续函数，则
A. $\int_0^{\int_0^1 e^{-t^2} \mathrm{~d} t} f(x) \mathrm{d} x \geqslant \int_0^1 f(x) \mathrm{e}^{-x^2} \mathrm{~d} x$ ．
B. $\int_0^{\int_0^1 e^{-t^2} \mathrm{~d} t} f(x) \mathrm{d} x \leqslant \int_0^1 f(x) \mathrm{e}^{-x^2} \mathrm{~d} x$ ．
C. $\int_0^{\int_0^1 e^{-t^2} \mathrm{~d} t} f(x) \mathrm{d} x \geqslant \int_0^1 f(x) \mathrm{d} x$ ．
D. $\int_0^{\int_0^1 e^{-t^2} \mathrm{~d} t} f(x) \mathrm{d} x \leqslant \int_0^1 f(x) \mathrm{d} x$ ．