Let $z_1$ and $z_2$ be two roots of the equation $z^2 + az + b = 0 , \; z$ being complex. Further, assume that the origin, $z_1$ and $z_2$ form an equilateral triangle. Then :

Question

( A ) $a^2 = 3b$
( B ) $a^2 = 2b$
( C ) $a^2 =b$
( D ) $a^2 = 4b$