Problem: FC Barcelona:

On 4 January 2016, Barcelona's transfer ban ended. The same day, they registered 77 players across all categories and ages, and both last summer signings Arda Turan and Aleix Vidal became eligible to play with the first team. On 10 February, qualifying for the sixth Copa del Rey final in the last eight seasons, Luis Enrique’s Barcelona broke the club's record of 28 consecutive games unbeaten in all competitions set by Guardiola’s team in the 2010–11 season, with a 1–1 draw with Valencia in the second leg of the 2015–16 Copa del Rey.

Besides Arda Turan, what other player became eligible to play in 2016?
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A: Aleix Vidal


Problem: In the former Soviet Union, electric traction eventually became somewhat more energy-efficient than diesel. Partly due to inefficient generation of electricity in the USSR (only 20.8% thermal efficiency in 1950 vs. 36.2% in 1975), in 1950 diesel traction was about twice as energy efficient as electric traction (in terms of net tonne-km of freight per kg of fuel). But as efficiency of electricity generation (and thus of electric traction) improved, by about 1965 electric railways became more efficient than diesel. After the mid 1970s electrics used about 25% less fuel per ton-km. However diesels were mainly used on single track lines with a fair amount of traffic  so that the lower fuel consumption of electrics may be in part due to better operating conditions on electrified lines (such as double tracking) rather than inherent energy efficiency. Nevertheless, the cost of diesel fuel was about 1.5 times more (per unit of heat energy content) than that of the fuel used in electric power plants (that generated electricity), thus making electric railways even more energy-cost effective.
How much fuel did electric train used less than diesel in the middle of 1970 in USSR?
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Answer: 25% less fuel per ton-km


Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
In 1997, the mammals were comprehensively revised by Malcolm C. McKenna and Susan K. Bell, which has resulted in the McKenna/Bell classification. Their 1997 book, Classification of Mammals above the Species Level, is the most comprehensive work to date on the systematics, relationships, and occurrences of all mammal taxa, living and extinct, down through the rank of genus, though recent molecular genetic data challenge several of the higher level groupings. The authors worked together as paleontologists at the American Museum of Natural History, New York. McKenna inherited the project from Simpson and, with Bell, constructed a completely updated hierarchical system, covering living and extinct taxa that reflects the historical genealogy of Mammalia.
Where did the two authors work together as paleontologist? 
A: American Museum of Natural History


Context and question: The lowest pressure that can be attained in a system is also dependent on many things other than the nature of the pumps. Multiple pumps may be connected in series, called stages, to achieve higher vacuums. The choice of seals, chamber geometry, materials, and pump-down procedures will all have an impact. Collectively, these are called vacuum technique. And sometimes, the final pressure is not the only relevant characteristic. Pumping systems differ in oil contamination, vibration, preferential pumping of certain gases, pump-down speeds, intermittent duty cycle, reliability, or tolerance to high leakage rates.
What are two other relevant characteristics of a pumping system along with final pressure?
Answer: oil contamination, vibration


Question: The winner receives a record deal with a major label, which may be for up to six albums, and secures a management contract with American Idol-affiliated 19 Management (which has the right of first refusal to sign all contestants), as well as various lucrative contracts. All winners prior to season nine reportedly earned at least $1 million in their first year as winner. All the runners-up of the first ten seasons, as well as some of other finalists, have also received record deals with major labels. However, starting in season 11, the runner-up may only be guaranteed a single-only deal. BMG/Sony (seasons 1–9) and UMG (season 10–) had the right of first refusal to sign contestants for three months after the season's finale. Starting in the fourteenth season, the winner was signed with Big Machine Records. Prominent music mogul Clive Davis also produced some of the selected contestants' albums, such as Kelly Clarkson, Clay Aiken, Fantasia Barrino and Diana DeGarmo. All top 10 (11 in seasons 10 and 12) finalists earn the privilege of going on a tour, where the participants may each earn a six-figure sum.
Is there an answer to this question: What does the winner of American Idol receive?

Answer: a record deal


Problem: Textual criticism:

When comparing different documents, or "witnesses", of a single, original text, the observed differences are called variant readings, or simply variants or readings. It is not always apparent which single variant represents the author's original work. The process of textual criticism seeks to explain how each variant may have entered the text, either by accident (duplication or omission) or intention (harmonization or censorship), as scribes or supervisors transmitted the original author's text by copying it. The textual critic's task, therefore, is to sort through the variants, eliminating those most likely to be un-original, hence establishing a "critical text", or critical edition, that is intended to best approximate the original. At the same time, the critical text should document variant readings, so the relation of extant witnesses to the reconstructed original is apparent to a reader of the critical edition. In establishing the critical text, the textual critic considers both "external" evidence (the age, provenance, and affiliation of each witness) and "internal" or "physical" considerations (what the author and scribes, or printers, were likely to have done).

Different documents that represent the same original text are called what?
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A:
witnesses