He Ended the persecution of Christians in the Roman empire and declared Christianity one of the religions approved by the emperor. He also eventually adopted the religion himself therefore increasing its credibility and decreasing the chance of new followers being persecuted.
I think because he says it would help them and give them more supplies.
C) Corrupt elections were common under Porfirio Diaz's regime, also known as the Porfiriato.
Although he ruled with a tight fist, and his country flourished during his reign, it was still illegal how he got to actually rule Mexico, because he established a dictatorship.
A. is the correct answer, because it has the most impact of all the others. A revolution overthrowing its current government means an entirely new nation, and is a turning point from the government before, and the new revolutionized country after.
Hope this helps!