Final answer:
The correct option is A. Julius Caesar was affiliated with the Populares, a political faction that supported the interests of Rome's landless proletariat and sought reforms challenging the traditional elite Optimates.
Step-by-step explanation:
The political party with which Julius Caesar was affiliated was the Populares. The Populares were a political faction that sought the support of the proletariat—Rome's landless working class—by advocating for reforms aimed at helping the disenfranchised. This stood in contrast to the Optimates, who represented the traditional Roman Senate elite and were in favor of maintaining the status quo.
Julius Caesar used his family ties to Marius and his military conquests to gain popularity among the Populares. His political strategies and alliances propelled him to power, notably forming part of the First Triumvirate alongside Pompey and Crassus to circumvent the political blockades set up by the Optimates.