Cystic fibrosis is a deadly disease of the lungs and digestive system. it is inherited as a recessive trait. how can two healthy parents have a child with cystic fibrosis?

The parents may possess the recessive trait. Let’s say both parents have the allele of Aa, where ‘a’ is the trait for cystic fibrosis, there is a chance that their child will posses the allele ‘aa’, meaning they would have the disease.

If you make it a little more clear i can answer it