If a pea plant has one dominant and one recessive form for height, how can the dwarf form appear in its offspring?

Correct answer: When the offspring receives recessive forms from both parents.

A plant with one dominant allele and one recessive allele is heterozygous and usually appears tall because the dominant allele masks the recessive one. It can nevertheless pass the recessive allele to a gamete. If an offspring receives one recessive allele from each parent, its genotype is homozygous recessive, so the dwarf phenotype is expressed. Thus option A is correct; receiving no gene is impossible and a dominant allele masks dwarfness.