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: Which PC operating environment sold more from Microsoft? Passage:Due to the sales growth of IBM clones in the '90s, they became the industry standard for business and home use. This growth was augmented by the introduction of Microsoft's Windows 3.0 operating environment in 1990, and followed by Windows 3.1 in 1992 and the Windows 95 operating system in 1995. The Macintosh was sent into a period of decline by these developments coupled with Apple's own inability to come up with a successor to the Macintosh operating system, and by 1996 Apple was almost bankrupt. In December 1996 Apple bought NeXT and in what has been described as a "reverse takeover", Steve Jobs returned to Apple in 1997. The NeXT purchase and Jobs' return brought Apple back to profitability, first with the release of Mac OS 8, a major new version of the operating system for Macintosh computers, and then with the PowerMac G3 and iMac computers for the professional and home markets. The iMac was notable for its transparent bondi blue casing in an ergonomic shape, as well as its discarding of legacy devices such as a floppy drive and serial ports in favor of Ethernet and USB connectivity. The iMac sold several million units and a subsequent model using a different form factor remains in production as of August 2017. In 2001 Mac OS X, the long-awaited "next generation" Mac OS based on the NeXT technologies was finally introduced by Apple, cementing its comeback.
 Links: a. USB b. Windows 3.0 c. Mac OS 8 d. Power Macintosh G3
Example Output: b

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 countries made up the group that invaded Yugoslavia? Passage:On 6 April 1941, Yugoslavia was invaded from all sides by the Axis powers, led by German forces. Stojanović was assigned as a physician to an infantry battalion based in Banja Luka. For several days after the invasion this battalion moved toward Dalmatia, before it completely disintegrated without fighting the enemy, and Stojanović returned to Prijedor. The Royal Yugoslav Army capitulated on 17 April, and the Axis powers proceeded to dismember Yugoslavia. Almost all of modern-day Croatia, all of modern-day Bosnia-Herzegovina, and parts of modern-day Serbia were combined into a puppet state called the Independent State of Croatia (, NDH). It was an "Italian-German quasi-protectorate", which was controlled by the fascist Ustaše led by Ante Pavelić. One of its policies was to eliminate the ethnic Serb population of the NDH through mass killings, expulsions and forced assimilation, and many Serbs fled from the NDH to the German-occupied territory of Serbia.
 Links: a. Axis powers b. Serbia c. Croatia d. Axis powers
Example Output:
a