The third answer is correct (C), Kiev.
Vladimir I, also known as Vladimir the Great, ruled Kievan from 980 to 1015 and was the first ruler of Kiev to officially establish orthodox Christianity as the new religion.
He took over the throne after overthrowing his brother Yaropolk in 978 and marrying the sister of the Byzantine emperor's emperor when he chased pagan icons and instituted the orthodox Catholic church in the state.