Concept:Self-pollination is enhanced when the flower's structure keeps pollen and stigma close within the same flower, especially when the flower does not open.
Explanation:Cleistogamy is the condition in which flowers remain closed and never open.
Because the flower stays closed, pollen cannot be carried away by wind or insects to another flower.
Therefore, pollen must land on the stigma of the same flower.
This condition guarantees self-pollination.
Heterostyly is the condition where stamens and styles are at different heights in different flowers.
This arrangement reduces the chance that pollen from a flower reaches the stigma of the same flower.
Protandry means the stamens mature before the stigma, so pollen is shed before the stigma becomes receptive.
Protogyny means the stigma matures before the stamens, so the stigma is receptive before pollen is released.
Both protandry and protogyny tend to prevent self-pollination and encourage cross-pollination.
Hence, among the options, only cleistogamy clearly enhances self-pollination.
Answer:A. Cleistogamy