Healthy parents have 2 children, a child with cystic fibrosis and a healthy child. They want to have another child. What are the chances of that child being a carrier?

The key is B. 1:2. [As the parents have a child with cystic fibrosis and they are healthy both of them are carrier. It is an autosomal recessive disease where if both parents are carrier mode of inheritence is as follows: Chance of being healthy child 1:4, Chance of being diseased 1:4 and chance of being carrier 1:2].