Limitation of the flooding tolerant rice varieties | Quick Homework Help

In many countries, plants face flooding stress especially around river basins, and due to flash floods, typhoons. Few days of complete submergence will negatively impact the growth and development of plants. It has been discovered that some rice varieties show flooding stress tolerance. In the flooding tolerant rice plants, the SUB1A (Submergence1) gene is activated when the plants are submerged. It results in effectively making the plant dormant, allowing it to conserve energy until the floodwater recedes. The rice varieties and species lacking the SUB1A gene have slowly disappeared from the flood-prone areas.
A) Did Flooding cause the appearance of the SUB1A gene to arise by mutation? If yes, explain how. If no give an alternative explanation for the appearance of the SUB1A gene in some rice varieties.
B) In a sentence or two explain what type of selection (directional, stabilizing or disruptive) is responsible for an increase in the more flooding-resistant rice varieties in the flooded areas?
C) Natural selection works at the population level to change allele frequencies. Explain briefly how this statement could be applied to the scenario above.
D) One limitation of the flooding-tolerant rice varieties is that they generally produce less seeds. What strategy would you use to generate flooding-tolerant rice plants which also produce more seeds?