$\frac{d}{dx} \{ \cos^{-1} (\frac{4x^3}{27} - x ) \}$ is equal to :

Question

( A ) $-\frac{1}{\sqrt{9-x^2}}$
( B ) $\frac{3}{\sqrt{9-x^2}}$
( C ) $\frac{1}{\sqrt{9-x^2}}$
( D ) $-\frac{3}{\sqrt{9-x^2}}$