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.
Q: Question: How long did the last Bulgarian Tsar rule the Empire? Passage:In Roman times, it was a village in the province of Moesia, first mentioned in 169. After the decline of the Roman Empire, the town turned out to be located at the northern border of the Byzantine Empire. In 1059, it was named Nicopolis, Greek for "City of Victory". During most of the Middle Ages, it was part of the Bulgarian Empire from its foundation in 681. After the fall of Tarnovo in 1393, the last Bulgarian Tsar Ivan Shishman defended what remained of the Empire from the fortress of Nikopol, where he was captured after the town was conquered by the Ottomans in 1395. Nikopol is therefore sometimes considered the capital of Bulgaria during these two years. It was the site of the Battle of Nicopolis, the last large-scale crusade of the Middle Ages, in 1396. At the fortress of Nicopolis, the united armies of Christian Europe headed by Hungarian king Sigismund and various French knights were defeated by the Ottomans under Bayezid I and his Serbian vassal Stefan Lazarevic.
Links: a. Kingdom of Hungary b. Battle of Nicopolis c. Ivan Shishman of Bulgaria d. Byzantine Empire
A:
c