Problem: Mexico City:

Mexico City remains the only Latin American city to host the Olympic Games, having held the Summer Olympics in 1968, winning bids against Buenos Aires, Lyon and Detroit. (This too will change thanks to Rio, 2016 Summer Games host). The city hosted the 1955 and 1975 Pan American Games, the last after Santiago and São Paulo withdrew. The ICF Flatwater Racing World Championships were hosted here in 1974 and 1994. Lucha libre is a Mexican style of wrestling, and is one of the more popular sports throughout the country. The main venues in the city are Arena México and Arena Coliseo.

What year did Mexico City first host the Pan America games?
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A: 1955


Problem: When a molten metal is mixed with another substance, there are two mechanisms that can cause an alloy to form, called atom exchange and the interstitial mechanism. The relative size of each element in the mix plays a primary role in determining which mechanism will occur. When the atoms are relatively similar in size, the atom exchange method usually happens, where some of the atoms composing the metallic crystals are substituted with atoms of the other constituent. This is called a substitutional alloy. Examples of substitutional alloys include bronze and brass, in which some of the copper atoms are substituted with either tin or zinc atoms. With the interstitial mechanism, one atom is usually much smaller than the other, so cannot successfully replace an atom in the crystals of the base metal. The smaller atoms become trapped in the spaces between the atoms in the crystal matrix, called the interstices. This is referred to as an interstitial alloy. Steel is an example of an interstitial alloy, because the very small carbon atoms fit into interstices of the iron matrix. Stainless steel is an example of a combination of interstitial and substitutional alloys, because the carbon atoms fit into the interstices, but some of the iron atoms are replaced with nickel and chromium atoms.
What two alloys is still a combination of?
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Answer: unanswerable


Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
The RCAF and Joint Task Force (North) (JTFN) also maintain at various points throughout Canada's northern region a chain of forward operating locations, each capable of supporting fighter operations. Elements of CF-18 squadrons periodically deploy to these airports for short training exercises or Arctic sovereignty patrols.
What patrols are organized from these locations?
A: Arctic sovereignty patrols.


Context and question: In 1886, Frank Julian Sprague invented the first practical DC motor, a non-sparking motor that maintained relatively constant speed under variable loads. Other Sprague electric inventions about this time greatly improved grid electric distribution (prior work done while employed by Thomas Edison), allowed power from electric motors to be returned to the electric grid, provided for electric distribution to trolleys via overhead wires and the trolley pole, and provided controls systems for electric operations. This allowed Sprague to use electric motors to invent the first electric trolley system in 1887–88 in Richmond VA, the electric elevator and control system in 1892, and the electric subway with independently powered centrally controlled cars, which were first installed in 1892 in Chicago by the South Side Elevated Railway where it became popularly known as the "L". Sprague's motor and related inventions led to an explosion of interest and use in electric motors for industry, while almost simultaneously another great inventor was developing its primary competitor, which would become much more widespread. The development of electric motors of acceptable efficiency was delayed for several decades by failure to recognize the extreme importance of a relatively small air gap between rotor and stator. Efficient designs have a comparatively small air gap. [a] The St. Louis motor, long used in classrooms to illustrate motor principles, is extremely inefficient for the same reason, as well as appearing nothing like a modern motor.
What was the name of Chicago's last electric trolley system?
Answer: unanswerable


Question: The region also experiences occasional periods of drought, during which the city sometimes has restricted water use by residents. During the late summer and early fall, Raleigh can experience hurricanes. In 1996, Hurricane Fran caused severe damage in the Raleigh area, mostly from falling trees. The most recent hurricane to have a considerable effect on the area was Isabel in 2003. Tornadoes also have on occasion affected the city of Raleigh most notably the November 28, 1988 tornado which occurred in the early morning hours and rated an F4 on the Fujita Tornado Scale and affected Northwestern portions of the city. Also the April 16, 2011 F3 Tornado which affected portions of downtown and North east Raleigh and the suburb of Holly Springs.
Is there an answer to this question: How big was the tornado in 2011?

Answer: F3


Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
Her fourth studio album 4 was released on June 28, 2011 in the US. 4 sold 310,000 copies in its first week and debuted atop the Billboard 200 chart, giving Beyoncé her fourth consecutive number-one album in the US. The album was preceded by two of its singles "Run the World (Girls)" and "Best Thing I Never Had", which both attained moderate success. The fourth single "Love on Top" was a commercial success in the US. 4 also produced four other singles; "Party", "Countdown", "I Care" and "End of Time". "Eat, Play, Love", a cover story written by Beyoncé for Essence that detailed her 2010 career break, won her a writing award from the New York Association of Black Journalists. In late 2011, she took the stage at New York's Roseland Ballroom for four nights of special performances: the 4 Intimate Nights with Beyoncé concerts saw the performance of her 4 album to a standing room only.
Beyonce's fourth album debuted in what year?
A:
2011