A Recessive Allele on the X Chromosome Is Responsible for Red-Green

A recessive allele on the X chromosome is responsible for red-green color blindness in humans.A woman with normal vision whose father is color blind marries a color-blind male.What is the probability that this couple's first son will be color blind?

A) 25%
B) 50%
C) about 66%
D) 75%
E) about 33%