Final answer:
Based on the military practices of similar ancient civilizations, it is most probable that the occupation of the Hittite soldier accompanying the driver in a chariot was that of an a) archer, who would utilize the bow and arrow for combat.
Step-by-step explanation:
The Hittite armies, like those of the Neo-Assyrian Empire, structured their forces for maximum effectiveness in warfare. A key component of these ancient armies were the chariots, which evolved from four-wheeled carts to more agile two-wheeled versions drawn by horses as mentioned in the references.
Neo-Assyrian fighters often assembled in squadrons of fifty chariots, with each chariot having a driver and an accompanying soldier.
While the occupation of the accompanying soldier is not mentioned for the Hittites specifically, the Neo-Assyrian Empire, which had similarities in military organization, did have specialized groups working together in battle.
These ancient chariots typically had an a) archer and a driver who would carry close-combat weapons such as swords and clubs.
Given the information provided, it's most probable that the Hittite soldier who would accompany a driver in a chariot would be an archer, using the bow and arrow to engage enemies at a distance while being mobile on the battlefield.