What might have contributed to the growth of christianity in the roman empire?

"Constantine's decision to cease the persecution of Christians in the Roman Empire was a turning point for Early Christianity, sometimes referred to as the Triumph of the Church, the Peace of the Church or the Constantinian shift. In 313, Constantine and Licinius issued the Edict of Milan decriminalizing Christian worship. The emperor became a great patron of the Church and set a precedent for the position of the Christian emperor within the Church and the notion of orthodoxy, Christendom, ecumenical councils and the state church of the Roman Empire declared by edict in 380. He is revered as a saint and is apostolic in the Eastern Orthodox Church and Oriental Orthodox Church for his example as a "Christian monarch."

The answer is c. good luck : )