The correct answer is: Cross the green-pod plant with a yellow-pod plant.
Yellow-pod plant phenotype is known to be homozygous recessive. In this case, we would use test cross to determine whether there are any recessive alleles in the unknown. The recessive homozygote (yellow-pod plant) will contribute an allele for the recessive characteristic to each offspring, the second allele (from the unknown genotype, green-pod plant) will determine the offspring's phenotype.
