# If $f:IR \to IR$ is defined by $f(x)=7+ \cos (5x+3)$ for $x \in IR,$ then the period of f is :

$\begin {array} {1 1} (a)\;2 \pi & \quad (b)\;\pi \\ (c)\;\frac{\pi}{5} & \quad (d)\;\frac{2 \pi}{5} \end {array}$

(d) $\frac{2\pi}{5}$