Problem: Group (mathematics):

To understand groups beyond the level of mere symbolic manipulations as above, more structural concepts have to be employed.c["] There is a conceptual principle underlying all of the following notions: to take advantage of the structure offered by groups (which sets, being "structureless", do not have), constructions related to groups have to be compatible with the group operation. This compatibility manifests itself in the following notions in various ways. For example, groups can be related to each other via functions called group homomorphisms. By the mentioned principle, they are required to respect the group structures in a precise sense. The structure of groups can also be understood by breaking them into pieces called subgroups and quotient groups. The principle of "preserving structures"a recurring topic in mathematics throughoutis an instance of working in a category, in this case the category of groups.

What has to be compatible with the group operation?
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A: constructions related to groups

Problem: Solar technologies are broadly characterized as either passive or active depending on the way they capture, convert and distribute sunlight and enable solar energy to be harnessed at different levels around the world, mostly depending on distance from the equator. Although solar energy refers primarily to the use of solar radiation for practical ends, all renewable energies, other than geothermal and tidal, derive their energy from the Sun in a direct or indirect way.
What is one way that characterizes solar technologies as passive or active?
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Answer: depending on the way they capture, convert and distribute sunlight

Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
The FBI has maintained files on numerous people, including celebrities such as Elvis Presley, Frank Sinatra, John Denver, John Lennon, Jane Fonda, Groucho Marx, Charlie Chaplin, the band MC5, Lou Costello, Sonny Bono, Bob Dylan, Michael Jackson, and Mickey Mantle. The files were collected for various reasons. Some of the subjects were investigated for alleged ties to the Communist party (Charlie Chaplin and Groucho Marx), or in connection with antiwar activities during the Vietnam War (John Denver, John Lennon, and Jane Fonda). Numerous celebrity files concern threats or extortion attempts against them (Sonny Bono, John Denver, John Lennon, Elvis Presley, Michael Jackson, Mickey Mantle, Groucho Marx, and Frank Sinatra).
Who was investigated for pro war activity?
A: unanswerable

Context and question: Israeli music contains musical influences from all over the world; Sephardic music, Hasidic melodies, Belly dancing music, Greek music, jazz, and pop rock are all part of the music scene. Among Israel's world-renowned orchestras is the Israel Philharmonic Orchestra, which has been in operation for over seventy years and today performs more than two hundred concerts each year. Israel has also produced many musicians of note, some achieving international stardom. Itzhak Perlman, Pinchas Zukerman and Ofra Haza are among the internationally acclaimed musicians born in Israel.[citation needed] Israel has participated in the Eurovision Song Contest nearly every year since 1973, winning the competition three times and hosting it twice. Eilat has hosted its own international music festival, the Red Sea Jazz Festival, every summer since 1987.
Who hosts its own international music festival every summer?
Answer: Eilat

Question: The Romans under Nero Claudius Drusus established a military outpost belonging to the Germania Superior Roman province at Strasbourg's current location, and named it Argentoratum. (Hence the town is commonly called Argentina in medieval Latin.) The name "Argentoratum" was first mentioned in 12 BC and the city celebrated its 2,000th birthday in 1988. "Argentorate" as the toponym of the Gaulish settlement preceded it before being Latinized, but it is not known by how long. The Roman camp was destroyed by fire and rebuilt six times between the first and the fifth centuries AD: in 70, 97, 235, 355, in the last quarter of the fourth century, and in the early years of the fifth century. It was under Trajan and after the fire of 97 that Argentoratum received its most extended and fortified shape. From the year 90 on, the Legio VIII Augusta was permanently stationed in the Roman camp of Argentoratum. It then included a cavalry section and covered an area of approximately 20 hectares. Other Roman legions temporarily stationed in Argentoratum were the Legio XIV Gemina and the Legio XXI Rapax, the latter during the reign of Nero.
Is there an answer to this question: What was the Roman camp destroyed by?

Answer: fire

Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
Initially the existing 5:3 aspect ratio had been the main candidate but, due to the influence of widescreen cinema, the aspect ratio 16:9 (1.78) eventually emerged as being a reasonable compromise between 5:3 (1.67) and the common 1.85 widescreen cinema format. An aspect ratio of 16:9 was duly agreed upon at the first meeting of the IWP11/6 working party at the BBC's Research and Development establishment in Kingswood Warren. The resulting ITU-R Recommendation ITU-R BT.709-2 ("Rec. 709") includes the 16:9 aspect ratio, a specified colorimetry, and the scan modes 1080i (1,080 actively interlaced lines of resolution) and 1080p (1,080 progressively scanned lines). The British Freeview HD trials used MBAFF, which contains both progressive and interlaced content in the same encoding.
What was a leading factor in the 16:9 aspect ratio being chosen?
A:
widescreen cinema