From the start of Japanese civilization until 1185 the emperor used to rule all Japan. An emperor was similar to a king, but in Japan he was also a religious leader. The emperor started to lose power in a series of wars. A civil war broke out in 1336 that ended the real power of the emperor. The emperor sent armies of samurai to fight the civil war for him, and when they returned he gave the title Shogun to the leader of the army. This idea of the Emperor had the goal of not giving the chance to the Samurai leader to be considered as emperor. This began a new form of control in Japan, where the leaders of different armies controlled smaller pieces of land, rather than one emperor controlling everything--this is usually called Feudal control (Feudalism).
So the answer to this question is:
A. the shogun
