Answer: B. Theodosius
Explanation: While Constantine by Milan Edict 313, made Christianity one of the religions of the Roman Empire, and thus equated it with other religions, Theodosius declared it the official religion of the Roman Empire.
Constantine did Christianity legal, but did not replace the traditional polytheistic Roman beliefs. At the First Council in 325, held in Nicaea, convened by Constantine, the Christian bishops decided which of the many Christian doctrines would be officially accepted and become the official version of Christianity, so called Orthodox Christianity.
Emperor Theodosius, by his Edict of Thessaloniki in 380, made Christianity the official religion of the Roman Empire, and all the doctrines rejected at the First Council in Nicaea were proclaimed a sect, lost their legal status and were forbidden.