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.

Example Input: Question: Who was older when Heitler obtained his doctorate, Arnold Sommerfeld or Karl Herzfeld? Passage:In 1922, Heitler began his study of physics at the Karlsruhe Technische Hochschule, in 1923 at the Humboldt University of Berlin, and in 1924 at the Ludwig Maximilian University of Munich (LMU), where he studied under both Arnold Sommerfeld and Karl Herzfeld. The latter was his thesis advisor when he obtained his doctorate in 1926; Herzfeld taught courses in theoretical physics and one in physical chemistry, and in Sommerfeld's absence often took over his classes. From 1926 to 1927, he was a Rockefeller Foundation Fellow for postgraduate research with Niels Bohr at the Institute for Theoretical Physics at the University of Copenhagen and with Erwin Schrödinger at the University of Zurich. He then became an assistant to Max Born at the Institute for Theoretical Physics at the University of Göttingen. Heitler completed his Habilitation, under Born, in 1929, and then remained as a Privatdozent until 1933. In that year, he was let go by the university because he was Jewish.
 Links: a. University of Göttingen b. Ludwig Maximilian University of Munich c. Arnold Sommerfeld d. Arnold Sommerfeld
Example Output: c

Example Input: Question: Who was the first to put forth the Voting Rights Act of 1965? Passage:In the United States, the Fifteenth Amendment to the United States Constitution, ratified in 1870 during the Reconstruction era, provided that "The right of citizens of the United States to vote shall not be denied or abridged by the United States or by any State on account of race, color, or previous condition of servitude." This amendment aimed to guarantee the right to vote to African Americans, many of whom had been enslaved in the South prior to the end (1865) of the American Civil War and the 1864-1865 abolition of slavery. Despite the amendment, however, blacks were disfranchised in the former Confederate states after 1877; Southern officials ignored the amendment and blocked black citizens from voting through a variety of devices, including poll taxes, literacy tests, and grandfather clauses; violence and terrorism were used to intimidate some would-be voters. Southern blacks did not effectively receive the right to vote until the Voting Rights Act of 1965.
 Links: a. Disenfranchisement after the Reconstruction Era b. Voting Rights Act of 1965 c. Reconstruction era d. African Americans
Example Output: b

Example Input: Question: When was the Aroostook War? Passage:The area was at the centre of the Aroostook War, a skirmish over boundary lines between the U.S.A. and what was then British North America. Originally confined to a disagreement between the State of Maine and the Colony of New Brunswick, the dispute eventually spread to involve the Government of the United States in Washington, D.C. and the British Colonial Administration in Quebec City, seat of the Governor General of Canada, who had supreme authority over all of British North America, including New Brunswick. In the wake of this international conflict, a small fortification (Fortin du Petit-Sault) was built in anticipation of a possible attack by the Americans, to complement the much larger fortification located at Fort Ingall (now Cabano) in nearby Canada (now Quebec). One of the central figures at the origin of the conflict was American-born industrialist "Colonel" John Baker, who had established sawmills and other lumber-related industries on the eastern shores of the Saint John river, an area claimed by the British that Baker wanted to be declared part of Maine as he was a fiercely nationalist American.
 Links: a. United States b. Aroostook War c. British North America d. Quebec
Example Output:
b