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 often are new issues of the Canadian Journal of Neurological Sciences published? Passage:Multi-dose versions of the vaccine contain the preservative thiomersal (also known as thimerosal), a mercury compound that prevents contamination when the vial is used repeatedly. Single-dose versions and the live vaccine do not contain this preservative. In the U.S., one dose from a multi-dose vial contains approximately 25 micrograms of mercury, a bit less than a typical tuna fish sandwich. In Canada, different variants contain five and 50 micrograms of thimerosal per dose. The use of thiomersal has been controversial, with claims that it can cause autism and other developmental disorders. The U.S. Institute of Medicine examined these claims and concluded in 2004 that the evidence did not support any link between vaccines and autism. Other reviews came to similar conclusions, with a 2006 review in the Canadian Journal of Neurological Sciences stating that there is no convincing evidence to support the claim that thimerosal has a causal role in autism, and a 2009 review in the journal Clinical Infectious Diseases stating that claims that mercury can cause autism are "biologically implausible". The U.K. National Health Service stated in 2003 that "There is no evidence of long-term adverse effects due to the exposure levels of thiomersal in vaccines." The World Health Organization concluded that there is "no evidence of toxicity in infants, children or adults exposed to thiomersal in vaccines". Indeed, in 2008 a review noted that even though thiomersal was removed from all US childhood vaccines in 2001, this has not changed the number of autism diagnoses, which are still increasing.
 Links: a. Thiomersal and vaccines b. Autism c. Canadian Journal of Neurological Sciences d. National Academy of Medicine
Example Output: c

Example Input: Question: Which is the oldest ancient religious text that mentions Tripura? Passage:Although there is no evidence of lower or middle Paleolithic settlements in Tripura, Upper Paleolithic tools made of fossil wood have been found in the Haora and Khowai valleys. The Indian epic, the Mahabharata; ancient religious texts, the Puranas; and the Edicts of Ashoka – stone pillar inscriptions of the emperor Ashoka dating from the third century BCE – all mention Tripura. An ancient name of Tripura is Kirat Desh (English: "The land of Kirat"), probably referring to the Kirata Kingdoms or the more generic term Kirata. However, it is unclear whether the extent of modern Tripura is coterminous with Kirat Desh. The region was under the rule of the Twipra Kingdom for centuries, although when this dates from is not documented. The Rajmala, a chronicle of Tripuri kings which was first written in the 15th century, provides a list of 179 kings, from antiquity up to Krishna Kishore Manikya (1830–1850), but the reliability of the Rajmala has been doubted.
 Links: a. Puranas b. Haora River c. Upper Paleolithic d. Khowai River
Example Output: a

Example Input: Question: Which club that Parish was loaned out to in 2011 was found first? Passage:Parish began his career at Aston Villa, where he progressed through the club's Academy. He made his professional debut away from the club on loan at League Two side Lincoln City in 2011, before a short loan at Cardiff City where he made no appearances. He joined Cardiff on a permanent basis in January 2012, before being loaned out to Wycombe Wanderers later the same year. He was released by the club in 2013, again failing to make a first-team appearance. He joined Bristol City, where he went on to make 19 league appearances, but again found himself out on loan, on this occasion to Newport County. He later joined Blackpool for one season, and then played for Colchester United for one season, before joining Accrington Stanley. He then signed for Dundee where he spent two seasons.
 Links: a. Colchester United F.C. b. Aston Villa Under-23s and Academy c. Lincoln City F.C. d. Dundee F.C.
Example Output:
c