The situations lead to the cross pollination is

Answer: Option D

The situations that lead to cross-pollination are Protandry, Heterostyly and herkogamy.
Protandry is the condition of flowers whose male parts mature before the female ones.
Heterostyly is a morphological and reproductive polymorphism in which plant populations are composed of two (distyly) or three (tristyly) floral morphs that differ reciprocally in the height of their stigmas and anthers.
Herkogamy is the spatial separation of the anthers and stigma in hermaphroditic angiosperms. It is a common strategy for reducing self-fertilization.
All the above condition increases the chances of cross-pollination in plants.