The correct option is A geitonogamy
Geitonogamy involves the transfer of pollen grains from a male flower to the stigma of another female flower growing on the same plant. Thus, geitonogamy operates only in monoecious plants, i.e., those plants having both the male and female flowers together in different places.
Autogamy refers to the self-pollination in which the transfer of the pollen grain occurs from the anther to the stigma within the same flower.
Cleistogamous flowers are those which do not open at all and hence, the pollen after dehiscence, fall onto the stigma of the same flower.
Xenogamy is the transfer of pollen grains of a flower to the stigma of another flower present on a different plant.