The answer is D.
Vladimir the Great was a grand prince of Kiev, and ruler of Kievan Rus from 980 to 1015.
Vladimir converted to Christianity in 988. Afterwards, he exhorted the residents of Kiev to the river for baptism. He asked all residents, "rich and poor, beggars and slaves" to come to the river, unless they wanted to become the prince's enemies. They were converted to Christianity, and this mass conversion started the Christianization of Kievan Rus.
i think you mean "who" not "what", so your answer is Vladimir.
Vladimir is the answer your looking for!
Vladimir is the guy that you need
“the battle of stalingrad is not a turning point necessarily in strategic terms, because a lot more has to be done before the soviets can be certain of defeating germany,” says renowned world war ii historian richard overy. the germans had fought nearly a thousand miles across the soviet union to get to stalingrad.