question_answer

A focus of an ellipse is at the origin. The directrix is the line x = 4 and the eccentricity is\[\frac{1}{2}\]. Then the length of the semi-major axis is

A)  \[\frac{2}{3}\]         

B)   \[\frac{4}{3}\]           

C)  \[\frac{5}{3}\]           

D)  \[\frac{8}{3}\]