Answer:

The correct answer is option 'B' - His sons.

The new military contingents were required to serve under the ruler's sons. This indicates a hereditary system of military leadership, where the ruler's sons were entrusted with the command and control of the military forces. This practice was common in many ancient civilizations and medieval kingdoms.

Explanation:

1. Hereditary Succession:
In many ancient and medieval societies, rulers often preferred to maintain a hereditary succession, where power and authority were passed down from the ruler to their offspring. This ensured stability and continuity in governance, as well as maintained the legitimacy of the ruling dynasty. The ruler's sons were groomed from a young age to take up leadership roles, including military command.

2. Military Leadership:
Military leadership was considered a crucial aspect of rulership, as it ensured the ruler's ability to defend and expand their territories. Therefore, it was essential for the ruler to have a capable and loyal military force under their command. By assigning their sons to lead military contingents, rulers could ensure their own interests were protected and their authority was upheld.

3. Loyalty and Succession:
Assigning the military contingents to the ruler's sons helped to secure the loyalty of the armed forces. The soldiers were more likely to be loyal to the ruler's family and the dynasty, as they saw themselves as part of the ruler's extended family. Moreover, by entrusting military command to their sons, rulers could ensure a smooth transition of power upon their demise, as the sons were already familiar with the military apparatus.

4. Training and Preparation:
The ruler's sons would often receive specialized training in military tactics, strategy, and leadership. They would be groomed from a young age to take up the responsibilities of military command. This training would ensure that the sons were prepared and capable of leading the military contingents effectively.

In conclusion, the new military contingents were required to serve under the ruler's sons due to the practice of hereditary succession, the importance of military leadership, the need for loyalty and succession, and the training and preparation received by the ruler's sons.