In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

Example Input: Factories in China often produce what type of gas in their emissions that acts as pollution?, Context: A dense wave of smog began in the Central and Eastern part of China on 2 December 2013 across a distance of around 1,200 kilometres (750 mi), including Tianjin, Hebei, Shandong, Jiangsu, Anhui, Shanghai and Zhejiang. A lack of cold air flow, combined with slow-moving air masses carrying industrial emissions, collected airborne pollutants to form a thick layer of smog over the region. The heavy smog heavily polluted central and southern Jiangsu Province, especially in and around Nanjing, with its AQI pollution Index at "severely polluted" for five straight days and "heavily polluted" for nine. On 3 December 2013, levels of PM2.5 particulate matter average over 943 micrograms per cubic metre, falling to over 338 micrograms per cubic metre on 4 December 2013. Between 3:00 pm, 3 December and 2:00pm, 4 December local time, several expressways from Nanjing to other Jiangsu cities were closed, stranding dozens of passenger buses in Zhongyangmen bus station. From 5 to 6 December, Nanjing issued a red alert for air pollution and closed down all kindergarten through middle schools. Children's Hospital outpatient services increased by 33 percent; general incidence of bronchitis, pneumonia, upper respiratory tract infections significantly increased. The smog dissipated 12 December. Officials blamed the dense pollution on lack of wind, automobile exhaust emissions under low air pressure, and coal-powered district heating system in North China region. Prevailing winds blew low-hanging air masses of factory emissions (mostly SO2) towards China's east coast.
Example Output: SO2

Example Input: Which has more prestige, the Spring Cup Series or low-tier NASCAR circuits?, Context: In addition to professional team sports, North Carolina has a strong affiliation with NASCAR and stock-car racing, with Charlotte Motor Speedway in Concord hosting two Sprint Cup Series races every year. Charlotte also hosts the NASCAR Hall of Fame, while Concord is the home of several top-flight racing teams, including Hendrick Motorsports, Roush Fenway Racing, Richard Petty Motorsports, Stewart-Haas Racing, and Chip Ganassi Racing. Numerous other tracks around North Carolina host races from low-tier NASCAR circuits as well.
Example Output: Sprint Cup Series

Example Input: What stage of development is after Old Persian in language origins?, Context: The other directly attested Old Iranian dialects are the two forms of Avestan, which take their name from their use in the Avesta, the liturgical texts of indigenous Iranian religion that now goes by the name of Zoroastrianism but in the Avesta itself is simply known as vohu daena (later: behdin). The language of the Avesta is subdivided into two dialects, conventionally known as "Old (or 'Gathic') Avestan", and "Younger Avestan". These terms, which date to the 19th century, are slightly misleading since 'Younger Avestan' is not only much younger than 'Old Avestan', but also from a different geographic region. The Old Avestan dialect is very archaic, and at roughly the same stage of development as Rigvedic Sanskrit. On the other hand, Younger Avestan is at about the same linguistic stage as Old Persian, but by virtue of its use as a sacred language retained its "old" characteristics long after the Old Iranian languages had yielded to their Middle Iranian stage. Unlike Old Persian, which has Middle Persian as its known successor, Avestan has no clearly identifiable Middle Iranian stage (the effect of Middle Iranian is indistinguishable from effects due to other causes).
Example Output:
Middle Persian