设 $I_1=\frac{\pi}{4} \int_0^{\frac{\pi}{4}} \frac{\tan x}{x} \mathrm{~d} x, I_2=\frac{4}{\pi} \int_0^{\frac{\pi}{4}} \frac{x}{\tan x} \mathrm{~d} x$, 则
$\text{A.}$ $I_1 < 1 < I_2$
$\text{B.}$ $1 < I_2 < I_1$
$\text{C.}$ $I_1 < I_2 < 1$
$\text{D.}$ $I_2 < 1 < I_1$