Final answer:
The area of the Roman Empire that is now France was known as Gaul during Roman times, and it is where the foundations of modern France were laid.
Step-by-step explanation:
The area of the Roman Empire that is now known as France was called Gaul. This region was integral to the Roman Empire following its conquest by Julius Caesar in the 50s BCE, and it played a significant role throughout the empire's history. The cultural and economic integration during Roman rule, known as Romanization, left a lasting impact on the region, shaping the unique culture that ultimately developed into modern France. After the decline of Roman power, the territory was ruled by the Franks, a Germanic people who established the kingdom that would become known as France.
The correct answer to the student's question is C. Gaul.