Let $\;a_{r}=\int\limits_{0}^{\frac{\pi}{4}}\;tan^{r}\;x\;dx$ , then $\;a_{1}+a_{3}\;,a_{2}+a_{4}\;,a_{3}+a_{5}\;$ are in

Question

$(a)\;AP\qquad(b)\;GP\qquad(c)\;HP\qquad(d)\;AGP$