Which genetic disorder cause the body to produce unusually thick mucus in the lungs and intestines?

Cystic fibrosis (CF) is a genetic (inherited) disease that causes sticky, thick mucus to build up in organs, including the lungs and the digestive system. In people who have CF, thick mucus clogs the airways and makes it difficult to breathe.

multiple allele inheritance is traits controlled by more than 2 alleles (ex: pigeons having 3 alleles of one gene govern their feather color).   so the answer is a.