Three-Factor Testcrosses Are Only Informative in Gene Mapping When Which

Three-factor testcrosses are only informative in gene mapping when which of the following occurs?

A) One parent is homozygous recessive for the three genes, and the other parent is homozygous dominant.
B) All three genes are located on separate chromosomes, and one parent is homozygous dominant for at least two of these genes.
C) Both parents are homozygous for the three genes.
D) One parent is heterozygous for the three genes, and the other parent is homozygous recessive.
E) One of the genes must be located on a sex chromosome and be heterozygous, and the other two genes must be located on an autosome and be homozygous.