Final answer:
Arianism was deemed heresy by mainline Christians and was not accepted at the Council of Nicaea.
Step-by-step explanation:
Arianism was a Germanic sect of Christianity that was deemed heresy by mainline Christians (answer A). It was not accepted as a viable form of Christianity at the Council of Nicaea (answer B). The spread of Arianism in the Roman Empire cannot be attributed to the work of the pope (answer C).
Learn more about Arianism