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: How old was the winner of the 18th season of Celebrity Big Brother when they won? Passage:The third series of the show began on 11 August 2015. The official list of cast members was released on 14 July 2015. This series was filmed in Cancun, Mexico, making this the first series to be filmed outside of Europe. They include four boys: Graham Griffiths, Jayden Robins, Kirk Norcross and Stephen Bear, and four girls: Amy Paige Cooke, Laura Alicia Summers, Megan McKenna and Megan Rees. With the announcement of the line-up it was confirmed that former Geordie Shore cast member and star of the first series, Vicky Pattison, would be making her return as an ex alongside Series 2 star Rogan O'Connor. The Only Way Is Essex cast member Kirk Norcross was also confirmed to be taking part in the series, with his ex-fiancée and Celebrity Big Brother star Cami-Li featuring as his ex. Star of Magaluf Weekender Jordan Davies was also revealed to be taking part in the series, also featuring as an ex. Megan McKenna and Jordan later returned for the fourth series. On 5 January 2016, cast member Megan McKenna entered the Celebrity Big Brother house to compete in the seveneeth series, and on 28 July 2016, Stephen Bear entered the house to compete in the eighteenth series where he left as the winner. Jordan Davies made another return to the show, this time during the fifth series with Jemma and Bear, and Holly also returning as an ex again. In August 2017, both Jemma Lucy and Jordan Davies took part in the twentieth series of Celebrity Big Brother.
 Links: a. Stephen Bear b. Stephen Bear c. The Only Way Is Essex d. Ibiza Weekender
Example Output: a

Example Input: Question: Which modernist sculptor is younger, Joseph Csaky or Jean Arp? Passage:In 1953, the foundation's collecting criteria expanded under its new director, James Johnson Sweeney. Sweeney rejected Rebay's dismissal of "objective" painting and sculpture, and he soon acquired Constantin Brâncuși's Adam and Eve (1921), followed by works of other modernist sculptors, including Joseph Csaky, Jean Arp, Calder, Alberto Giacometti and David Smith. Sweeney reached beyond the 20th century to acquire Paul Cézanne's Man with Crossed Arms (c. 1899). The same year, the foundation also received a gift of 28 important works from the Estate of Katherine S. Dreier, a founder of America's first collection to be called a modern art museum, the Société Anonyme. Dreier had been a colleague of Rebay's. The works included Little French Girl (1914–18) by Brâncuși, an untitled still life (1916) by Juan Gris, a bronze sculpture (1919) by Alexander Archipenko and three collages (1919–21) by German Hanoverian Dadaist Schwitters. It also included works by Calder, Marcel Duchamp, El Lissitzky and Mondrian. Among others, Sweeney also acquired the works of Alberto Giacometti, David Hayes, Willem de Kooning and Jackson Pollock.
 Links: a. Joseph Csaky b. Jackson Pollock c. Constantin Brâncuși d. Marcel Duchamp
Example Output: a

Example Input: Question: How long did the German invasion of Soviet Union that Hannig participated in last? Passage:Born in 1921 in Frankenstein, Lower Silesia, Hannig joined the military service in the Luftwaffe as a Fahnenjunker (officer cadet) in October 1939. He was posted to the 6./Jagdgeschwader 54 "Grünherz" (JG 54—54th fighter wing) in early 1941. His brother, Walter Hannig, received the German Cross in Gold () on 28 April 1943 as an observer with Aufklärungsgruppe (reconnaissance group) 4.(F)/14 of the Luftwaffe. Horst Hannig claimed his first aerial victory, a Tupolev SB-2, on the first day of Operation Barbarossa, the German invasion of the Soviet Union on 22 June 1941. He achieved his first 30 victories up to November 1941. On 9 May 1942, Leutnant (second Lieutenant) Hannig was awarded the Knight's Cross of the Iron Cross () having flown over 200 operations and claiming 48 victories. He and Leutnant Hans Beißwenger received the Knight's Cross from General der Flieger Helmuth Förster at Siverskaya. On 21 July 1942 he claimed his 54th victory, a Petlyakov Pe-2 reconnaissance aircraft, near Lake Ilmen. It was JG 54 2,500th aerial victory.
 Links: a. Petlyakov Pe-2 b. Lower Silesia c. Operation Barbarossa d. Jagdgeschwader 54
Example Output:
c