Color blindness is caused by an X-linked recessive gene. A color-blind man and a woman with normal vision whose father was color blind have a son. The probability that their son is color blind is:
A) 0.25 (or 25 percent). B) 0.50 (or 50 percent). C) 0.75 (or 75 percent). D) 1.00 (or 100 percent). E) none of these.