Which, If Any, of the Following Is Incorrect? When Used

Which, if any, of the following is incorrect? When used in human genetics, the term heterozygote

A) applies even if a person possesses two alleles that differ by just one nucleotide out of a million
B) consistently applies to Y-specific loci because men must be heterozygotes at these loci, having a very different sequence on the X chromosome.
C) may apply to a person with a recessive disease when the two mutant alleles are not identical.
D) does not apply to loci on the X chromosome in women because in each of a woman's cells one X chromosome is inactivated.