What are the genotypes of the parents of a child with cystic fibrosis if both parents have normal phenotypes?

If both parents have normal phenotypes but have a child with cystic fibrosis, they are most likely carriers of the cystic fibrosis gene. The genotypes of the parents would be heterozygous (Cf/cf), where "Cf" represents the allele for cystic fibrosis and "cf" represents the normal allele. This means each parent carries one copy of the cystic fibrosis allele and one normal allele, allowing for the possibility of having an affected child (cf/cf) when both parents pass on the recessive allele.