If $(1+\tan A)(1+\tan B)=2$ find all values of $A+B$

Question

$\begin{array}{1 1}(A)\;n\pi+\large\frac{\pi}{4}&(B)\;n\pi+ \large\frac{\pi}{6}\\(C)\;n\pi+ \large\frac{\pi}{8}&(D)\;2n\pi+\large\frac{3\pi}{4}\end{array}$