A couple has a child with cystic fibrosis, an autosomal recessive disease. ... ...

A couple has a child with cystic fibrosis, an autosomal recessive disease. Neither parent has the disease. Another child is born, who is unaffected. What is the probability that this unaffected child is a carrier of cystic fibrosis? A. 1/4 B. 1/2 C. 2/3 D. 3/4
(A) Column A is larger
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in 19. Genetics