How did the Romans adopt other religions?

Nicene Christianity

In 380 CE, the emperor Theodosius issued the Edict of Thessalonica, which made Christianity, specifically Nicene Christianity, the official religion of the Roman Empire. Most other Christian sects were deemed heretical, lost their legal status, and had their properties confiscated by the Roman state.The official Roman religion was the worship of a large group of Greco Roman gods such a Jupiter, Juno, Minerva and Mars. A Roman priest was responsible for the proper ritual worship to the gods. The very success of the Roman Empire proved that the Romans had properly worshiped their gods.Over time, the Christian church and faith grew more organized. In 313 AD, the Emperor Constantine issued the Edict of Milan, which accepted Christianity: 10 years later, it had become the official religion of the Roman Empire.

Explanation:

d) a constitutional amendment

i believe the answer is d.