An organism can be homozygous dominant if it carries two copies of the same dominant allele, or homozygous recessive if it carries two copies of the same recessive allele. Heterozygous means that an organism has two different alleles of a gene. Offspring can be developed by the fusion of gametes of both parents. If the results of a test cross reveal that all the offspring resemble the parent being tested. This parent must be homozygous because all the gametes of parents carry the same allele that fuses to form same offsprings. Thus, the correct answer is option B.