C. A is incorrect because if they have the disease then they cannot be healthy. B is incorrect because if the genetic disease is recessive then the cannot have the homozygous mutated gene because then it would mean that they are ill. D is incorrect because having an offspring that is ill doesn't always guarantee that all the offspring will be ill.
For a child to inherit a recessive genetic disease like sickle cell anemia, both healthy parents must be carriers of the mutated gene. This means they possess one normal allele and one mutated allele, allowing the child a chance to inherit the disease if they receive the mutated allele from both parents. Therefore, the correct answer is option C.
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