Both autogamy and geitonogamy are prevented in:

The correct option is B Papaya
If pollination occurs within the same flower, then, it is called autogamy and if it occurs in different flowers of the same plant, then, it is called geitonogamy.

Both geitonogamy and autogamy do not occur in papaya as it is a dioecious (male and female flowers are present in different plants) plant that contains unisexual flowers (a flower has either male or female parts).

Castor, maize and cucumber have unisexual flowers but, they are monoecious (male and female flowers are present in the same plant). Hence autogamy will not occur in these plants but, geitonogamy can occur.