If `veca,vecb,vecc` be three that unit vectors such that `vecaxx(vecbxxvecc)=1/2 vecb, vecb and vecc

If `veca,vecb,vecc` be three that unit vectors such that `vecaxx(vecbxxvecc)=1/2 vecb, vecb and vecc` veing non parallel. If `theta_1` is the angle between `veca and vecb` and `theta_2` is the angle between `veca and vecb` then (A) `theta_1 = pi/6, theta_2=pi/3` (B) `theta_1 = pi/3, theta_2=pi/6` (C) `theta_1 = pi/2, theta_2=pi/3` (D) `theta_1 = pi/3, theta_2=pi/2`