Concept:Successful reproduction after pollination depends on genetic compatibility between the two plants.Explanation:Pollination is the transfer of pollen from the male part to the female part of a flower.For fertilisation and seed formation to take place, the pollen must be accepted by the stigma.This acceptance occurs only when the pollen comes from a plant of the same species.If plants P and Q belong to different species, pollination usually fails and reproduction does not occur.Answer:Plants P and Q should be of the same species.Correct option: A.