Among the situations given below, choose the one that prevents both autogamy and geitonogamy.
Monoecious plant bearing unisexual flowers
Dioecious plant bearing only male or female flowers
Monoecious plant with bisexual flowers
Dioecious plant with bisexual flowers
Dioecious plants (bearing only male or female flowers) both autogamy and geitonogamy are prevented.