Answer: C
Explanation:
The total number of steps that are required to reach $\mathbf {(m, n)}$ is $\color {green} {\underline {\mathbf {\color {red} {{m+n}}}}}$. So, $\mathbf m$ steps are required on the $\mathbf x-\text{axis}$ and $\mathbf n$ steps are required on the $\mathbf y-\text{axis}$.
From $\mathbf {m+n}$ stride, the number of steps which are taken on the $\mathbf x-\text{axis}$ and $\mathbf y-\text{axis}$ can be distributed in any way.
$\therefore $ If $\mathbf n$ steps are chosen on the $\mathbf y-\text{axis}$, then the remaining steps should go to the $\mathbf x -\text{axis}$.
$\therefore$ Total steps $=\fbox {$\Large \color {blue} {\mathbf {\binom{m+n}{n}}}$}$
$\therefore$ C is the correct option.