Why Are Men More Likely to Be Red/green Color Blind

Why are men more likely to be red/green color blind?

A) Men have fewer photoreceptors with M and L opsins.
B) M and L opsins are located close to each other on the X chromosome.
C) Testosterone modulates the absorption of M and L opsins.
D) M and L opsins probably evolved from a common ancestor.
How Are Signals from Rods and Cones Analyzed in the Retina?