JEE Math Practice Question

Let $f: \mathbf{R} \rightarrow \mathbf{R}$ be defined as : $$ f(x)= \begin{cases}\frac{a-b \cos 2 x}{x^2} ; & x1\end{cases} $$ If $f$ is continuous everywhere in $\mathbf{R}$ and $m$ is the number of points where $f$ is NOT differential then $\mathrm{m}+\mathrm{a}+\mathrm{b}+\mathrm{c}$ equals :

1. A.1
2. B.4
3. C.3
4. D.2