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 high is the gamma radiation from nuclear fuel? Passage:The nuclear fuel elements were made of refractory ceramic based on beryllium oxide, with enriched uranium dioxide as fuel and small amount of zirconium dioxide for structural stability. The fuel elements were hollow hexagonal tubes about long with distance between the outer parallel planes, with inside diameter of . They were manufactured by high-pressure extruding of the green compact, then sintering almost to its theoretical density. The core consisted of 465,000 individual elements stacked to form 27,000 airflow channels; the design with small unattached elements reduced problems related with thermal stresses. The elements were designed for average operation temperature of ; the autoignition temperature of the reactor base plates was only 150 °C higher. The neutron flux was calculated to be 9×10 neutrons/(cm·s) in the aft and 7×10 neutrons/(cm·s) in the nose. The gamma radiation level was fairly high due to the lack of shielding; radiation hardening for the guidance electronics had to be designed.
 Links: a. Beryllium oxide b. Radiation hardening c. Nuclear fuel d. Radiation hardening
Example Output: c

Example Input: Question: Which professional ice hockey league that McNab ever played in was formed first? Passage:After playing junior hockey in Saskatoon, Saskatchewan, McNab played on the Omaha Knights of the USHL in the 1946–48 season before being called up to the Detroit Red Wings of the National Hockey League in 1947. He would play on and off with the Red Wings until 1951, playing on the team that won the Stanley Cup in 1950. He played for the Indianapolis Capitols of the American Hockey League in 1950–51. Before the 1951–52 season, he was traded by the Red Wings to the Chicago Black Hawks, but never played for the team. Back surgery kept him out of action in 1951–52 and McNab then joined the New Westminster Royals of the Western Hockey League, where he played for seven seasons, retiring in 1959. He was voted league MVP in 1955, scoring 32 goals and 81 points.
 Links: a. Omaha Knights (AHA) b. Saskatoon c. National Hockey League d. United States Hockey League (1945–1951)
Example Output: d

Example Input: Question: Which of the three emperors who Ji served lived longest? Passage:Jiang Ji (died 18 May 249), courtesy name Zitong, was an official and military general of the state of Cao Wei during the Three Kingdoms period of China. Born in the late Eastern Han dynasty, Jiang Ji started his career as a low-level official in his native Yang Province before becoming a subordinate of Cao Cao, the warlord who controlled the central government towards the end of the Eastern Han dynasty. After the end of the Eastern Han dynasty, he served in the state of Cao Wei through the reigns of the first three emperors – Cao Pi, Cao Rui and Cao Fang – and held various appointments in the military before rising to Grand Commandant, one of the top positions in the central government. During his service in Wei, he was known for being candid in giving advice to the emperor on various issues, including consolidating power, halting labour-intensive construction projects, and officials' abuses of power. In February 249, he joined the regent Sima Yi in staging a successful coup d'état against his co-regent Cao Shuang, but died from illness a few months later.
 Links: a. Cao Pi b. Cao Shuang c. Courtesy name d. Incident at the Gaoping Tombs
Example Output:
a