The correct option is D Homogamy
Homogamy is a condition wherein the male and the female reproductive organs mature at the same time. This condition is very essential for self-pollination to take place.
Apart from homogamy, unisexuality of a flower, dicogamy (ripening of male and female organs at different timings), and heterostyly ( differences in length of stigma and anthers such that they can not reciprocate) favour cross-pollination.