Answer: D. They were able to store and preserve a surplus of food for times of need.
Step-by-step explanation:
One of the key ways that Han Emperors were able to keep their empire stable was by implementing effective agricultural policies, such as improving irrigation systems and encouraging farmers to cultivate new crops. These policies allowed for a surplus of food to be stored and preserved for times of need, such as famine or drought, which helped to prevent food shortages and maintain social stability.
In addition to their agricultural policies, Han Emperors also implemented a range of other measures to keep their empire stable, such as promoting Confucianism as a unifying philosophy, establishing a centralized bureaucracy to administer the government, and promoting the development of trade and commerce. These measures helped to create a stable and prosperous society that lasted for centuries.
Therefore, option D, "They were able to store and preserve a surplus of food for times of need" is the correct answer.