The correct option is C Xenogamy
In xenogamy, pollen grains from a different plant of the same species are transferred to stigma. Hence, this type of pollination brings genetically different types of pollen grains to the stigma.
In autogamy, pollen grains are transferred to the stigma of the same flower. In geitonogamy, the transfer of pollen grains is between different flowers of the same plant. Therefore the pollen grains which are transferred to the stigma are genetically similar in both autogamy and geitonogamy.