If $x, y, z$ are in A.P and $\tan^{-1}x. \tan^{-1}y$ and $\tan^{-1}z$ are also in A.P., then

Question

( A ) $2x = 3y = 6z$
( B ) $x = y = z$
( C ) $6x = 4y = 3z$
( D ) $6x = 3y = 2z$