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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 many major fighting parties were there in the War of the Breton Succession? Passage:Thomas of Woodstock was in command of a large campaign in northern France that followed the War of the Breton Succession of 134364. The earlier conflict was marked by the efforts of John IV, Duke of Brittany to secure control of the Duchy of Brittany against his rival Charles of Blois. John was supported in this struggle by the armies of the kingdom of England, whereas Charles was supported by the kingdom of France. At the head of an English army, John prevailed after Charles was killed in battle in 1364, but the French continued to undermine his position, and he was later forced into exile in England. He returned to Brittany in 1379, supported by Breton barons who feared the annexation of Brittany by France. An English army was sent under Woodstock to support his position. Due to concerns about the safety of a longer shipping route to Brittany itself, the army was ferried instead to the English continental stronghold of Calais in July 1380. As Woodstock marched his 5,200 men east of Paris, they were confronted by the army of Philip the Bold, Duke of Burgundy, at Troyes, but the French had learned from the Battle of Crecy in 1346 and the Battle of Poitiers in 1356 not to offer a pitched battle to the English. Eventually, the two armies simply marched away. French defensive operations were then thrown into disarray by the death of King Charles V of France on 16 September 1380. Woodstock's chevauchee continued westwards largely unopposed, and in November 1380 he laid siege to Nantes and its vital bridge over the Loire towards Aquitaine. However, he found himself unable to form an effective stranglehold, and urgent plans were put in place for Sir Thomas Felton to bring 2,000 reinforcements from England. By January, though, it had become apparent that the duke of Brittany was reconciled to the new French king Charles VI, and with the alliance collapsing and dysentery ravaging his men, Woodstock abandoned the siege.
Links: a. Calais b. Troyes c. War of the Breton Succession d. Charles, Duke of Brittany
Output:
c