In this task, you're given a question, a context passage, and four options which are terms from the passage. After reading a passage, you will get a brief understanding of the terms. Your job is to determine by searching and reading further information of which term you can answer the question. Indicate your choice as 'a', 'b', 'c', or 'd'. If you think more than one option is plausible, choose the more probable option to help you answer the question.

Question: How long did the state entity that Macedonia was the political heart of last? Passage:In 1014, after decades of war, the Byzantine Emperor Basil II scored a decisive victory over the Bulgarian Emperor Samuil in the battle of Kleidion. Samuil died of a heart attack on 6 October 1014 and the Byzantines took the opportunity to penetrate deep into Macedonia, the political heart of the Bulgarian Empire, and seized a number of important cities (Bitola, Prilep, Voden, Maglen). After the new Bulgarian Emperor Ivan Vladislav, who in 1015 assassinated Samuil's son and heir Gavril Radomir, had unsuccessfully tried to make an agreement with Basil II, he organized the defense of the country. The Bulgarians led by the Emperor, Krakra of Pernik and Ivats managed to return a number of towns and castles. The Byzantines were defeated in the battle of Bitola (September 1015) and at the siege of Pernik (summer of 1016).
Links: a. Basil II b. Ivan Vladislav of Bulgaria c. First Bulgarian Empire d. Prilep
c