As we know a recessesvie trait to be expressed the organism must be homozygous for the recessive allele, otherwise, it will be masked by the dominant allele, now Huntington's disease is a dominant disorder meanwhile, achondroplasia has an autosomal dominant pattern but does not follow a simple mendelian inheritance pattern, which left us cystic fibrosis, that is an inherited recessive disorder, therefore this is the correct answer (optionC).
