The statement that best evaluates why Constantine I converted to Christianity during his fight to gain control of the Roman Empire is: "Constantine thought he saw a cross in the sky the night before a big battle and believed this celestial clue helped him win the battle."
This reflects the significant event reported in historical accounts where Constantine experienced a vision of a cross and, following that, attributed his victory in the Battle of Milvian Bridge in 312 AD to divine intervention, which played a key role in his eventual conversion to Christianity.