While Europe was struggling with the Dark Ages, and a feudal system that failed to develop wealth for any but the most privileged families regardless of merit, the Abbasid Khalifate expanded the iqta system of reward for military leaders in a way that dramatically increased agricultural production, while encouraging innovation, rewarding effort, and requiring respectful treatment of those who would spend their lives working the land. The iqta system encouraged these soldier/ landowners to maximize the productivity of their land. The Empire owned the land but it was granted to soldiers who had been successful. It could be taken back if these soldiers did a bad job of working the land, or even if they were unfair or cruel to their workers. Very importantly, these grants of land were not hereditary, although they could be bought and sold. All of this meant that the existing land of the Islamic world would be used more efficiently, yielding larger harvests, all while ensuring that citizens working the land were treated with respect. This was a feat of social engineering that has never been equaled, even today. Choice A is the correct answer.