Problem: Printed circuit board:

Unpopulated boards are usually bare-board tested for "shorts" and "opens". A short is a connection between two points that should not be connected. An open is a missing connection between points that should be connected. For high-volume production a fixture or a rigid needle adapter is used to make contact with copper lands on the board. Building the adapter is a significant fixed cost and is only economical for high-volume or high-value production. For small or medium volume production flying probe testers are used where test probes are moved over the board by an XY drive to make contact with the copper lands. The CAM system instructs the electrical tester to apply a voltage to each contact point as required and to check that this voltage appears on the appropriate contact points and only on these.

A closed is a missing connection between what?
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A: unanswerable


Problem: Railways must operate at variable speeds. Until the mid 1980s this was only practical with the brush-type DC motor, although such DC can be supplied from an AC catenary via on-board electric power conversion. Since such conversion was not well developed in the late 19th century and early 20th century, most early electrified railways used DC and many still do, particularly rapid transit (subways) and trams. Speed was controlled by connecting the traction motors in various series-parallel combinations, by varying the traction motors' fields, and by inserting and removing starting resistances to limit motor current.
All early electrified motors used what type of motor?
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Answer: unanswerable


Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
This law is a fundamental principle of physics. As shown rigorously by Noether's theorem, the conservation of energy is a mathematical consequence of translational symmetry of time, a property of most phenomena below the cosmic scale that makes them independent of their locations on the time coordinate. Put differently, yesterday, today, and tomorrow are physically indistinguishable. This is because energy is the quantity which is canonical conjugate to time. This mathematical entanglement of energy and time also results in the uncertainty principle - it is impossible to define the exact amount of energy during any definite time interval. The uncertainty principle should not be confused with energy conservation - rather it provides mathematical limits to which energy can in principle be defined and measured.
What shows that the conservation of energy is a mathematical consequence of translational symmetry of time?
A: Noether's theorem


Context and question: Advances were made in irrigation and farming, using new technology such as the windmill. Crops such as almonds and citrus fruit were brought to Europe through al-Andalus, and sugar cultivation was gradually adopted by the Europeans. Arab merchants dominated trade in the Indian Ocean until the arrival of the Portuguese in the 16th century. Hormuz was an important center for this trade. There was also a dense network of trade routes in the Mediterranean, along which Muslim countries traded with each other and with European powers such as Venice, Genoa and Catalonia. The Silk Road crossing Central Asia passed through Muslim states between China and Europe.
What cultivation was gradually adopted by Muslims>
Answer: unanswerable


Question: Her debut single, "Crazy in Love" was named VH1's "Greatest Song of the 2000s", NME's "Best Track of the 00s" and "Pop Song of the Century", considered by Rolling Stone to be one of the 500 greatest songs of all time, earned two Grammy Awards and is one of the best-selling singles of all time at around 8 million copies. The music video for "Single Ladies (Put a Ring on It)", which achieved fame for its intricate choreography and its deployment of jazz hands, was credited by the Toronto Star as having started the "first major dance craze of both the new millennium and the Internet", triggering a number of parodies of the dance choreography and a legion of amateur imitators on YouTube. In 2013, Drake released a single titled "Girls Love Beyoncé", which featured an interpolation from Destiny Child's "Say My Name" and discussed his relationship with women. In January 2012, research scientist Bryan Lessard named Scaptia beyonceae, a species of horse fly found in Northern Queensland, Australia after Beyoncé due to the fly's unique golden hairs on its abdomen. In July 2014, a Beyoncé exhibit was introduced into the "Legends of Rock" section of the Rock and Roll Hall of Fame. The black leotard from the "Single Ladies" video and her outfit from the Super Bowl half time performance are among several pieces housed at the museum.
Is there an answer to this question: How many copies did Crazy in Love sell?

Answer: around 8 million copies


QUES: Three-phase AC railway electrification was used in Italy, Switzerland and the United States in the early twentieth century. Italy was the major user, for lines in the mountainous regions of northern Italy from 1901 until 1976. The first lines were the Burgdorf-Thun line in Switzerland (1899), and the lines of the Ferrovia Alta Valtellina from Colico to Chiavenna and Tirano in Italy, which were electrified in 1901 and 1902. Other lines where the three-phase system were used were the Simplon Tunnel in Switzerland from 1906 to 1930, and the Cascade Tunnel of the Great Northern Railway in the United States from 1909 to 1927.

The four-phase system was used in what tunnel in Switzerland?
What is the answer?
ANS:
unanswerable