Where Should the CR Enter the Patient for the AP $\frac{1}{2}$

Where should the CR enter the patient for the AP projection of the knee?

A) $\frac{1}{2}$ inch below the apex of the patella
B) inch below the base of the patella
C) 1 inch distal to the medial epicondyle of the femur
D) 1 $\frac{1}{2}$ inch proximal to the medial epicondyle of the femur