From among the situations given below, choose the one that prevents both autogamy and geitonogamy.

In Autogamy, pollination is achieved within the same flower, i.e., it is type of self pollination. In this the pollens are transferred from anther to stigma of same flower.

Geitonogamy is pollination where pollination is achieved by transfer of pollen grains from anther to stigma of another flower of same plant.

So, Dioecious plant having only male or female flowers both autogamy and geitonogamy is not possible. As either stigma will be absent or anther will be absent.

Hence, Dioecious plant bearing only male or female flowers prevents both autogamy and geitonogamy.

Therefore the correct answer is option (b).