If $1, \omega, \omega^2$ are the roots of unity, then $(a+b)^3 + (a \omega + b \omega^2)^3 + (a \omega^2 +b \omega)^3$ is equal to :

Question

( A ) $3(a^3 + b^3)$
( B ) $a^3 +b^3 + 3ab$
( C ) $a^2 -b^3$
( D ) $a^3+b^3$