The correct answer is A. Dichogamy.
Dichogamy is a type of sexual dimorphism in which the male and female reproductive organs of a flower mature at different times. This prevents self-pollination and increases the chances of cross-pollination.
Herpogamy is a type of pollination in which the pollen grains are transferred from the anthers of one flower to the stigma of another flower by an animal, such as an insect or a bird.
Haterogamy is a type of sexual reproduction in which the male and female gametes are produced by different individuals.
In a bisexual flower, the androecium (male part) and the gynoecium (female part) are present in the same flower. If the androecium and gynoecium mature at different times, it is called dichogamy. This prevents self-pollination and increases the chances of cross-pollination.