Problem: Railway electrification system:

The key advantage of the four-rail system is that neither running rail carries any current. This scheme was introduced because of the problems of return currents, intended to be carried by the earthed (grounded) running rail, flowing through the iron tunnel linings instead. This can cause electrolytic damage and even arcing if the tunnel segments are not electrically bonded together. The problem was exacerbated because the return current also had a tendency to flow through nearby iron pipes forming the water and gas mains. Some of these, particularly Victorian mains that predated London's underground railways, were not constructed to carry currents and had no adequate electrical bonding between pipe segments. The four-rail system solves the problem. Although the supply has an artificially created earth point, this connection is derived by using resistors which ensures that stray earth currents are kept to manageable levels. Power-only rails can be mounted on strongly insulating ceramic chairs to minimise current leak, but this is not possible for running rails which have to be seated on stronger metal chairs to carry the weight of trains. However, elastomeric rubber pads placed between the rails and chairs can now solve part of the problem by insulating the running rails from the current return should there be a leakage through the running rails.

What has a tendency to flow past nearby iron pipes forming the water and gas mains?
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A: unanswerable


Problem: Animal:

Animals have several characteristics that set them apart from other living things. Animals are eukaryotic and multicellular, which separates them from bacteria and most protists. They are heterotrophic, generally digesting food in an internal chamber, which separates them from plants and algae. They are also distinguished from plants, algae, and fungi by lacking rigid cell walls. All animals are motile, if only at certain life stages. In most animals, embryos pass through a blastula stage, which is a characteristic exclusive to animals.

What sets animals apart from bacteria  and most protists?
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A: Animals are eukaryotic and multicellular


Problem: House music:

The term "house music" is said to have originated from a Chicago club called The Warehouse, which existed from 1977 to 1983. Clubbers to The Warehouse were primarily black and gay, who came to dance to music played by the club's resident DJ Frankie Knuckles, whom fans refer to as the "godfather of house". After the Warehouse closed in 1983, the crowds went to Knuckles' new club, The Power Plant. In the Channel 4 documentary Pump Up The Volume, Knuckles remarks that the first time he heard the term "house music" was upon seeing "we play house music" on a sign in the window of a bar on Chicago's South Side. One of the people in the car with him joked, "you know, that's the kind of music you play down at the Warehouse!", and then everybody laughed. South-Side Chicago DJ Leonard "Remix" Roy, in self-published statements, claims he put such a sign in a tavern window because it was where he played music that one might find in one's home; in his case, it referred to his mother's soul & disco records, which he worked into his sets. Farley Jackmaster Funk was quoted as saying "In 1982, I was DJing at a club called The Playground and there was this kid named Leonard 'Remix' Roy who was a DJ at a rival club called The Rink. He came over to my club one night, and into the DJ booth and said to me, 'I've got the gimmick that's gonna take all the people out of your club and into mine – it's called House music.' Now, where he got that name from or what made him think of it I don't know, so the answer lies with him."

What city was the club The Remix located in?
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A: unanswerable


Problem: IPod:

On October 22, 2007, Apple reported quarterly revenue of US$6.22 billion, of which 30.69% came from Apple notebook sales, 19.22% from desktop sales and 26% from iPod sales. Apple's 2007 year revenue increased to US$24.01 billion with US$3.5 billion in profits. Apple ended the fiscal year 2007 with US$15.4 billion in cash and no debt.

What was the value of Apple's cash assets at the end of 2007?
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A:
$15.4 billion