The eccentricity of an ellipse, with its centre at the origin, is $\frac{1}{2}$. If one of the directrices is $x=4$, then the equation of the ellipse is

Question

( A ) $3x^2+4y^2=12$
( B ) $4x^2+3y^2=1$
( C ) $4x^2+3y^2=12$
( D ) $3x^2+4y^2=1$