To solve this problem, we need to understand the types of pollination and how they are prevented in dioecious plants.$\newline \bullet$Dioecious plants have male and female flowers on separate plants.$\newline \bullet$Autogamy refers to self-pollination within the same flower.$\newline \bullet$Geitonogamy refers to pollination between different flowers of the same plant.$\newline \bullet$Xenogamy refers to cross-pollination between flowers of different plants.$\newline$In dioecious plants:$\newline \bullet$Autogamy is prevented because male and female flowers are on separate plants, so self-pollination within the same flower cannot occur.$\newline \bullet$Geitonogamy is also prevented because there are no male and female flowers on the same plant, so pollination between flowers of the same plant is not possible.$\newline$Therefore, a dioecious flowering plant prevents both autogamy and geitonogamy.$\newline$This corresponds to Option 1: Autogamy and geitonogamy.