If $u =x + y$ and $v = x^2 - y^2$, then $\begin {vmatrix} \frac{ \partial u}{ \partial x} & \frac{ \partial u}{ \partial y} \\ \frac{ \partial v}{ \partial x} & \frac{ \partial v}{ \partial y} \end{vmatrix}$ is equal to :

Question

( A ) $v$
( B ) $u$
( C ) $u+v$
( D ) $-2u$