If $\overrightarrow a\:\:and\:\:\overrightarrow b$ are two unit vectors such that $\overrightarrow a+2\overrightarrow b\:\:and\:\:5\overrightarrow a-4\overrightarrow b$ are $\perp$ to each other, then the angle between $\overrightarrow a\:\:and\:\:\overrightarrow b$ is?

Question

$\begin{array}{1 1} (A) \large\frac{\pi}{6}\\ (B) \large\frac{\pi}{4}\\ (C) \large\frac{\pi}{3} \\ (D) \cos^{-1}\large\frac{2}{7} \end{array}$