If $z= \log (\tan x +\tan y)$, then $(\sin 2x) \large\frac{\partial z}{\partial x}$$+(\sin 2y) \large\frac{\partial z}{\partial y}$ is equal to

Question

\[\begin {array} {1 1} (a)\;1 & \quad (b)\;2 \\ (c)\;3 & \quad (d)\;4 \end {array}\]