Input: Read this: 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.
Question: What heavy metal group introduced darker themes to the music?

Output: Black Sabbath

Input: Read this: Most modern air defence systems are fairly mobile. Even the larger systems tend to be mounted on trailers and are designed to be fairly quickly broken down or set up. In the past, this was not always the case. Early missile systems were cumbersome and required much infrastructure; many could not be moved at all. With the diversification of air defence there has been much more emphasis on mobility. Most modern systems are usually either self-propelled (i.e. guns or missiles are mounted on a truck or tracked chassis) or easily towed. Even systems that consist of many components (transporter/erector/launchers, radars, command posts etc.) benefit from being mounted on a fleet of vehicles. In general, a fixed system can be identified, attacked and destroyed whereas a mobile system can show up in places where it is not expected. Soviet systems especially concentrate on mobility, after the lessons learnt in the Vietnam war between the USA and Vietnam. For more information on this part of the conflict, see SA-2 Guideline.
Question: What systems are really geared toward mobility?

Output: Soviet

Input: Read this: From the 2011 Census, the Office for National Statistics published that Plymouth's unitary authority area population was 256,384; 15,664 more people than that of the last census from 2001, which indicated that Plymouth had a population of 240,720. The Plymouth urban area had a population of 260,203 in 2011 (the urban sprawl which extends outside the authority's boundaries). The city's average household size was 2.3 persons. At the time of the 2011 UK census, the ethnic composition of Plymouth's population was 96.2% White (of 92.9% was White British), with the largest minority ethnic group being Chinese at 0.5%. The white Irish ethnic group saw the largest decline in its share of the population since the 2001 Census (-24%), while the Other Asian and Black African had the largest increases (360% and 351% respectively). This excludes the two new ethnic groups added to the 2011 census of Gypsy or Irish Traveller and Arab. The population rose rapidly during the second half of the 19th century, but declined by over 1.6% from 1931 to 1951.
Question: What was the average number of people in a Plymouth household?

Output: 2.3

Input: Read this: This meagre statistic expanded in the 20th century to comprise anthropology departments in the majority of the world's higher educational institutions, many thousands in number. Anthropology has diversified from a few major subdivisions to dozens more. Practical anthropology, the use of anthropological knowledge and technique to solve specific problems, has arrived; for example, the presence of buried victims might stimulate the use of a forensic archaeologist to recreate the final scene. Organization has reached global level. For example, the World Council of Anthropological Associations (WCAA), "a network of national, regional and international associations that aims to promote worldwide communication and cooperation in anthropology", currently contains members from about three dozen nations.
Question: From how many nations does the WCAA boast members from?

Output:
about three dozen