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.

Ex Input:
Question: How many people died in the incident that contaminated about 30,000 km?  Passage:Natural strontium is a mixture of four stable isotopes: Sr, Sr, Sr, and Sr. Their abundance increases with increasing mass number and the heaviest, Sr, makes up about 82.6% of all natural strontium, though the abundance varies due to the production of radiogenic Sr as the daughter of long-lived beta-decaying Rb. Of the unstable isotopes, the primary decay mode of the isotopes lighter than Sr is electron capture or positron emission to isotopes of rubidium, and that of the isotopes heavier than Sr is electron emission to isotopes of yttrium. Of special note are Sr and Sr. The former has a half-life of 50.6 days and is used to treat bone cancer due to strontium's chemical similarity and hence ability to replace calcium. While Sr (half-life 28.90 years) has been used similarly, it is also an isotope of concern in fallout from nuclear weapons and nuclear accidents due to its production as a fission product. Its presence in bones can cause bone cancer, cancer of nearby tissues, and leukemia. The 1986 Chernobyl nuclear accident contaminated about 30,000 km with greater than 10 kBq/m with Sr, which accounts for 5% of the core inventory of Sr.
 Links: a. Rubidium b. Mass number c. Electron capture d. Chernobyl disaster

Ex Output:
d


Ex Input:
Question: When was the college founded where Beloff earned a degree in chemistry? Passage:Anne Beloff was born in 1921 in Hampstead to Simon Beloff and Marie Katzin. Her parents were of Russian–Jewish background, and her siblings included the historian Max Beloff, Baron Beloff, the psychologist John Beloff, the journalist Nora Beloff, and the politician Renee Soskin. She earned a degree in chemistry from University College London in 1942 before completing a PhD in the biochemistry of skin burns with Rudolph Peters at the University of Oxford. She visited Harvard Medical School in 1946 to perform research and returned to the UK in 1948. In the same year she married Ernst Boris Chain, a biochemist who had won the Nobel Prize in Physiology or Medicine in 1945, and moved with him to Rome.
 Links: a. Max Beloff, Baron Beloff b. University College London c. Ernst Chain d. Nora Beloff

Ex Output:
b


Ex Input:
Question: Is the fort that Runyon took more than 2,000 pictures of still operational? Passage:Runyon opened a commercial photography studio in 1910. He initially photographed urban life Brownsville and Matamoros, Tamaulipas and the surrounding terrain of the Rio Grande Valley. In 1913, Runyon began recording the events of the Mexican Revolution, starting with the takeover of the Matamoros garrison by the Constitutional Army under General Lucio Blanco on June 3. He traveled with Blanco's forces to Ciudad Victoria and later Monterrey. In 1915, Runyon was the only professional to photograph two skirmishes by Mexican bandits on American soil, the Norias Ranch Raid and a train derailment near Olmito, Texas. He took more than 2,000 pictures of Fort Brown, which captured troop buildup and mechanization in preparation for World War I. Runyon returned to more traditional subjects in the border region, as well as portraits and postcards, following the end of the war.
 Links: a. Bandit War b. Fort Brown c. Rio Grande Valley d. Raid on Norias Ranch

Ex Output:

b