After the victory in the battle over his rival for the Roman throne, Emperor Constantine took the necessary steps for convening and assembling the Milan Edict in 313 years. According to this edict, Christianity has become an equal religion with all the existing official religions of the Roman Empire. The persecution of Christians ceased and thus ended the era of early Christianity. Shortly thereafter in Nicaea in 326, the First Ecumenical Council was held on the topic of formalization of Biblical gospels, scriptures and beliefs, thus establishing the official New Testament.
The answer is: D.