What is a two- point test cross, involving a dihybrid F1 fly, used for when mapping genes?

A) to determine if the F1 fly is homozygous dominant or heterozygous
B) to determine the allele combinations that a homozygous recessive fly can create
C) to determine which alleles are dominant and which are recessive
D) to determine the recombination frequency between two genes
E) to determine the allele combinations that the F1 fly can produce