You will be given a definition of a task first, then some input of the task.
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 old was Gabriel Bethlen when his forces sacked Vienna? Passage:At the time, the Thirty Years' War was raging across Europe. Gabriel Bethlen, prince of Transylvania saw an opportunity to unite the two Hungarian principalities, Transylvania and Royal Hungary, and sacked Vienna in November 1619. He also asked Sultan Osman II for aid, but this was unsuccessful. The Commonwealth was relatively uninvolved in this war but the Polish king, Zygmunt III Waza, sent an elite and ruthless mercenary unit, the Lisowczycy, to aid his Habsburg allies. They defeated the Hungarian lord George Rakoczi at the Battle of Humenne in 1619, and thus, cut the supply lines of Transylvanian forces. Then Gaspar Graziani, ruler of Moldavia, switched sides and joined Poland.
Links: a. Gabriel Bethlen b. George I Rakoczi c. George I Rakoczi d. Gaspar Graziani
Output:
a