A Recessive Gene for Red-Green Color Blindness Is Located on the X

A recessive gene for red-green color blindness is located on the X chromosome in humans.Assume that a woman with normal vision (her father is color blind) marries a color-blind male.What is the likelihood that this couple's first son will be color blind?

A) 0%
B) 25%
C) 50%
D) 75%
E) 100%