Q: What is a question about this article? If the question is unanswerable, say "unanswerable".
In the late 1960s, the term heavy metal was used interchangeably with hard rock, but gradually began to be used to describe music played with even more volume and intensity. While hard rock maintained a bluesy rock and roll identity, including some swing in the back beat and riffs that tended to outline chord progressions in their hooks, heavy metal's riffs often functioned as stand-alone melodies and had no swing in them. Heavy metal took on "darker" characteristics after Black Sabbath's breakthrough at the beginning of the 1970s. In the 1980s it developed a number of subgenres, often termed extreme metal, some of which were influenced by hardcore punk, and which further differentiated the two styles. Despite this differentiation, hard rock and heavy metal have existed side by side, with bands frequently standing on the boundary of, or crossing between, the genres.
Which term was never used interchangeably with hard rock?
A: unanswerable

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The traditional parish system persisted until the Reconstruction Era, when counties were imposed.[citation needed] Nevertheless, traditional parishes still exist in various capacities, mainly as public service districts. When the city of Charleston was formed, it was defined by the limits of the Parish of St. Philip and St. Michael, now also includes parts of St. James' Parish, St. George's Parish, St. Andrew's Parish, and St. John's Parish, although the last two are mostly still incorporated rural parishes.
What other parish besides St. John's Parish is mostly an incorporated urban parish?
A: unanswerable

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Bohr also introduced the quantity , now known as the reduced Planck constant, as the quantum of angular momentum. At first, Bohr thought that this was the angular momentum of each electron in an atom: this proved incorrect and, despite developments by Sommerfeld and others, an accurate description of the electron angular momentum proved beyond the Bohr model. The correct quantization rules for electrons in which the energy reduces to the Bohr model equation in the case of the hydrogen atom were given by Heisenberg's matrix mechanics in 1925 and the Schrodinger wave equation in 1926: the reduced Planck constant remains the fundamental quantum of angular momentum. In modern terms, if J is the total angular momentum of a system with rotational invariance, and Jz the angular momentum measured along any given direction, these quantities can only take on the values
Who helped to give the correct quantization rules for electrons in 1925?
A: Heisenberg

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The dogs' value to early human hunter-gatherers led to them quickly becoming ubiquitous across world cultures. Dogs perform many roles for people, such as hunting, herding, pulling loads, protection, assisting police and military, companionship, and, more recently, aiding handicapped individuals. This impact on human society has given them the nickname "man's best friend" in the Western world. In some cultures, however, dogs are also a source of meat.
Dogs had a worth to what type of early humans?
A:
hunter-gatherers