A plant having either dominant or recessive allele of a gene is said to be pure breeding or homozygous for that gene or trait. Due to the presence of both same type of allele, pure-breeding plants produce progeny of their own kind. A cross pollination of two unrelated plants produces heterozygous plants having one dominant and one recessive allele for a gene. Pure breeding plants are obtained by self-pollination only. Therefore, the correct answer is option A.