Integrate: $Un =\int \limits_0^{\large\frac{\pi}{4}} \tan ^n x dx$, find $U_n+U_{n-2}$

Question

$$\begin {array} {1 1} (a)\;\frac{1}{n-1} \\ (b)\;\frac{1}{n+2} \\ (c)\;\frac{1}{n-3} \\ (d)\;\frac{1}{n+4} \end {array}$$