Final answer:
The Roman roads facilitated the spread of early Christianity by enabling missionaries to travel and communicate more effectively across the Empire. Constantine's conversion and subsequent policy changes by later emperors also made Christianity the dominant religion, influencing society and governance. So, the cod.rrect answer is option
Step-by-step explanation:
What contributed most to the spread of early Christianity was not the Rome's exemption of Christians from paying taxes, Emperor Nero's conversion and enforced conversion, nor was it through military force by Christian armies. Instead, the facilitation of communication and travel by the Roman roads played a crucial role in spreading ideas and religions, including Christianity, more quickly throughout the Empire.
Before Constantine's conversion, Christianity grew through missionary work, without seriously disrupting polytheism or the Empire's religious diversity. However, the official endorsement of Christianity by Emperor Constantine linked secular power to Christian identity, making it a way for individuals to advance within the Roman power structure.
The subsequent Christianization of the state by Emperor Theodosius I in the fourth century and the eventual alignment of Christianity with imperial policy shifted societal norms and practices significantly away from polytheism towards monotheism.