When Mendel crossed the pollen from a plant with green pods with a plant with yellow seed pods, all of the offspring had green seed pods. This told him that

All offsprings had yellow peas

Answer: This told him that the allele for a green pod is dominant to the allele for yellow pods.

Explanation: Dominant traits will express themselves even if the allele for the other trait is there. If all of the offspring were green even though they carried the allele for a yellow pod, green must be dominant.