Answer:
The correct answer is b: Constantine I made Christianity a legally recognized faith.
Explanation:
Constantine I was born in what is nowadays Serbia, circa 280. He became Roman Emperor in 324 and was the first emperor who would adhere to Christianity, after a vision he had had while looking at the sky in the battle of Milvian Bridge (312) - this vision was, for him, a victory promise, so he had his soldiers' shields painted with the first two letters of Christ's name.
That was what led him to issue the Edict of Milan in 313 - Christianity's status was raised and legalized - Christians then could worship God all around the Empire. Despite this fact, he didn't convert to Christianity all of a sudden, but he was a patron for the Church, and became a Christian later in 337, on his deathbed.
