33. If $a + \beta = \pi / 2$ and $\beta + \gamma = a$, then tan $a$ equals:\\ (A) $2 ( \tan \beta + \tan \gamma )$\\ (B) $\tan \beta + \tan \gamma$\\ (C) $\tan \beta + 2 \tan \gamma$\\ (D) $2 \tan \beta + \tan \gamma$\\