An Individual Single Gene Disorder Can Show Different Levels of Genetic

An individual single gene disorder can show different levels of genetic heterogeneity, and different mutations in a single gene can sometimes result in a very wide range of different phenotypes. Which, if any, of the following statements, is false?

A) Allelic heterogeneity describes a situation where any of a range of different mutations in one gene can result in the same disorder
B) Sickle cell anemia is an outstanding example of allelic heterogeneity.
C) Locus heterogeneity means that a disease phenotype is manifest only as a result of the additive contributions of genetic variants at multiple loci.
D) The situation where different mutations in a single gene result in quite different diseases can be described as phenotype heterogeneity.