Final answer:
The Pax Romana and the Roman roads facilitated the spread of Christianity throughout most of Europe. Therefore, the correct option is A. Christianity throughout most of Europe.
Step-by-step explanation:
The Pax Romana and the vast extension of Roman roads facilitated the spread of Christianity throughout most of Europe. The rise of Christianity in the Roman Empire marked a turning point, and with the support of the government, it quickly spread across the empire. The Roman roads provided the infrastructure for the movement of people and ideas, allowing Christianity to reach new regions.