The value of \ ( m^2 + n^2 ) ( m - n ) - ( m - n )^3 \ ( m^2n - mn^2 ) is:

Answer: Option C

$$\begin{array}{rl}& \frac{\left\{\left(m^2+n^2\right)\left(m-n\right)-{\left(m-n\right)}^3\right\}}{\left(m^{2}n-m{n}^2\right)}\\ & =\frac{\left(m-n\right)\left[m^2+n^2-{\left(m-n\right)}^2\right]}{mn\left(m-n\right)}\\ & =\frac{m^2+n^2-m^2-n^2+2mn}{mn}\\ & =\frac{2mn}{mn}\\ & =2\text{ Answer}\end{array}$$