Solve: $(x+y)(dx-dy)=dx+dy.$[Hint:Substitute x+y=z after separating dx and dy]

Question

$\begin{array}{1 1}(A)\;c\;e^{\large y+x}=x+y \\(B)\;c\;e^{\large x-y}=x+y \\(C)\;c\;e^{\large y-x}=x+y \\(D)\;c\;e^{\large y-x}=x-y \end{array}$