Problem: San Diego:

San Diego is served by the San Diego Trolley light rail system, by the SDMTS bus system, and by Coaster and Amtrak Pacific Surfliner commuter rail; northern San Diego county is also served by the Sprinter light rail line. The Trolley primarily serves downtown and surrounding urban communities, Mission Valley, east county, and coastal south bay. A planned Mid-Coast extension of the Trolley will operate from Old Town to University City and the University of California, San Diego along the I-5 Freeway, with planned operation by 2018. The Amtrak and Coaster trains currently run along the coastline and connect San Diego with Los Angeles, Orange County, Riverside, San Bernardino, and Ventura via Metrolink and the Pacific Surfliner. There are two Amtrak stations in San Diego, in Old Town and the Santa Fe Depot downtown. San Diego transit information about public transportation and commuting is available on the Web and by dialing "511" from any phone in the area.

What number can you dial from any phone for public transportation information in San Francisco?
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A: unanswerable

Problem: Before the establishment of the Modern Greek state, the link between ancient and modern Greeks was emphasized by the scholars of Greek Enlightenment especially by Rigas Feraios. In his "Political Constitution", he addresses to the nation as "the people descendant of the Greeks". The modern Greek state was created in 1829, when the Greeks liberated a part of their historic homelands, Peloponnese, from the Ottoman Empire. The large Greek diaspora and merchant class were instrumental in transmitting the ideas of western romantic nationalism and philhellenism, which together with the conception of Hellenism, formulated during the last centuries of the Byzantine Empire, formed the basis of the Diafotismos and the current conception of Hellenism.
What did Greeks do that caused the formation of the new state ?
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Answer: the Greeks liberated a part of their historic homelands, Peloponnese, from the Ottoman Empire

Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
Arthur Collier published similar assertions though there seems to have been no influence between the two contemporary writers. The only knowable reality is the represented image of an external object. Matter as a cause of that image, is unthinkable and therefore nothing to us. An external world as absolute matter unrelated to an observer does not exist as far as we are concerned. The universe cannot exist as it appears if there is no perceiving mind. Collier was influenced by An Essay Towards the Theory of the Ideal or Intelligible World by "Cambridge Platonist" John Norris (1701).
When was An Essay Towards the Theory of the Ideal or Intelligible World written?
A: 1701

Context and question: The city's first bus rapid transit line, the Metrobus, began operation in June 2005, along Avenida Insurgentes. Line 2 opened in December 2008, serving Eje 4 Sur, line 3 opened in February 2011, serving Eje 1 Poniente, and line 4 opened in April 2012 connecting the airport with San Lazaro and Buenavista Station at Insurgentes. As the microbuses were removed from its route, it was hoped that the Metrobus could reduce pollution and decrease transit time for passengers. In June 2013, Mexico City's mayor announced two more lines to come: Line 5 serving Eje 3 Oriente and Line 6 serving Eje 5 Norte. As of June 2013, 367 Metrobus buses transported 850,000 passengers daily.
When did the second line of Metrobus open?
Answer: December 2008

Question: During World War II, the development of the anti-aircraft proximity fuse required an electronic circuit that could withstand being fired from a gun, and could be produced in quantity. The Centralab Division of Globe Union submitted a proposal which met the requirements: a ceramic plate would be screenprinted with metallic paint for conductors and carbon material for resistors, with ceramic disc capacitors and subminiature vacuum tubes soldered in place. The technique proved viable, and the resulting patent on the process, which was classified by the U.S. Army, was assigned to Globe Union. It was not until 1984 that the Institute of Electrical and Electronics Engineers (IEEE) awarded Mr. Harry W. Rubinstein, the former head of Globe Union's Centralab Division, its coveted Cledo Brunetti Award for early key contributions to the development of printed components and conductors on a common insulating substrate. As well, Mr. Rubinstein was honored in 1984 by his alma mater, the University of Wisconsin-Madison, for his innovations in the technology of printed electronic circuits and the fabrication of capacitors.
Is there an answer to this question: During World War I, the development of the anti-aircraft proximity fuse required what?

Answer: unanswerable

Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
Depleted uranium is also used as a shielding material in some containers used to store and transport radioactive materials. While the metal itself is radioactive, its high density makes it more effective than lead in halting radiation from strong sources such as radium. Other uses of depleted uranium include counterweights for aircraft control surfaces, as ballast for missile re-entry vehicles and as a shielding material. Due to its high density, this material is found in inertial guidance systems and in gyroscopic compasses. Depleted uranium is preferred over similarly dense metals due to its ability to be easily machined and cast as well as its relatively low cost. The main risk of exposure to depleted uranium is chemical poisoning by uranium oxide rather than radioactivity (uranium being only a weak alpha emitter).
What trait causes depleted uranium to be used in gyroscopic compasses?
A:
high density