John and Sarah had a child born with cystic fibrosis, a genetic disease. Both John and Sarah were normal, showing no signs of this disorder. How is it possible for them to have a child with this disease? a. Cystic fibrosis must be a dominant trait disorder hidden in both parents' genotype, but not showing in the phenotype, that could be passed on to offspring.

b. Cystic fibrosis must be a recessive trait disorder hidden in both parents’ genotype, but not showing in the phenotype, that could be passed on to offspring.

c. Cystic fibrosis must be a dominant trait disorder hidden in one parents’ genotype, but not showing in the phenotype, that could be passed on to offspring.

d. Cystic fibrosis must be a recessive trait disorder hidden in one parents’ genotype, but not showing in the phenotype, that could be passed on to offspring