Answer the following question: Information:  - A civil engineer is a person who practices civil engineering  the application of planning, designing, constructing, maintaining, and operating infrastructures while protecting the public and environmental health, as well as improving existing infrastructures that have been neglected.  - The Avro 552 was a British light biplane aircraft produced in the early 1920s. It was another attempt by Avro to sell a derivative of the wartime 504 to the civil market.  - An autogyro (from Greek  + , "self-turning"), also known as gyroplane, gyrocopter, or rotaplane, is a type of rotorcraft that uses an unpowered rotor in autorotation to develop lift, and an engine-powered propeller, similar to that of a fixed-wing aircraft, to provide thrust. While similar to a helicopter rotor in appearance, the autogyro's rotor must have air flowing through the rotor disc to generate rotation. Invented by the Spanish engineer Juan de la Cierva to create an aircraft that could fly safely at slow speeds, the autogyro was first flown on 9 January 1923, at Cuatro Vientos Airfield in Madrid. De la Cierva's aircraft resembled the fixed-wing aircraft of the day, with a front-mounted engine and propeller in a tractor configuration to pull the aircraft through the air.  - A bomber is a combat aircraft designed to attack ground and sea targets by dropping air-to-ground weaponry, firing torpedoes or deploying air-launched cruise missiles.  - The Cold War was a state of political and military tension after World War II between powers in the Eastern Bloc (the Soviet Union and its satellite states) and powers in the Western Bloc (the United States, its NATO allies and others). Historians do not fully agree on the dates, but a common timeframe is the period (the second half of the 20th century) between 1947, the year the Truman Doctrine (a U.S. policy pledging to aid nations threatened by Soviet expansionism) was announced, and 1991, the year the Soviet Union collapsed.  - The Avro Lancaster is a British four-engined Second World War heavy bomber designed and built by Avro for the Royal Air Force (RAF). It first saw active service with RAF Bomber Command in 1942 and, as the strategic bombing offensive over Europe gathered momentum, it was the central implement for the night-time bombing campaigns that followed. It became the main heavy bomber used by the RAF, the RCAF, and squadrons from other Commonwealth and European countries serving within the RAF, overshadowing its close contemporaries the Handley Page Halifax and Short Stirling. The "Lanc", as it was affectionately known, thus became one of the more famous and most successful of the Second World War night bombers, "delivering 608,612 long tons of bombs in 156,000 sorties." The Lancaster, an evolution of the troublesome Avro Manchester, was designed by Roy Chadwick and was powered by four Rolls-Royce Merlins, or, in one version, Bristol Hercules engines.  - Juan de la Cierva y Codorníu, 1st Count of De La Cierva (21 September 1895 in Murcia, Spain  9 December 1936 in Croydon, United Kingdom) was a Spanish civil engineer, pilot and aeronautical engineer. His most famous accomplishment was the invention in 1920 of the "Autogiro", a single-rotor type of aircraft that came to be called autogyro in the English language. In 1923, after four years of experimentation, De la Cierva developed the articulated rotor, which resulted in the world's first successful flight of a stable rotary-wing aircraft, with his C.4 prototype.  - The Cierva C.8 was an experimental autogiro built by Juan de la Cierva in England in 1926 in association with Avro . Like Cierva 's earlier autogiros , the C.8s were based on existing fixed - wing aircraft fuselages - in this case , the Avro 552 . The first example , the C.8R ( known to Avro as the Type 587 ) was a rebuild of the C.6D , fitted with stub wings and paddle - shaped main rotor blades . This was followed by the new - built C.8V ( or Type 586 ) that was eventually converted back into an Avro 552 after testing . The next model was the definitive C.8L prototype ( or Type 575 ) . The Mark II was based on the Lynx - engined Avro 504N 2 - seat trainer . By now , Cierva 's efforts were attracting the attention of buyers . The first customer was the British Air Ministry , which placed an order for a machine in 1927 . This was completed as the Type 611 , test flown by Bert Hinkler at Hamble and then delivered to the Royal Aircraft Establishment by Cierva himself in Britain 's first cross-country rotorcraft flight on 30 September that year . The next example was purchased by Air Commodore James G. Weir , chairman of Cierva , and flown in the 1928 King 's Cup Air Race before being used to make demonstration flights around continental Europe . The two final C.8s were sold in 1928 , one to the Italian government , and one to American Harold Pitcairn , who would go on to purchase manufacturing rights for the United States . The C.8W bought by Pitcairn would make the first autogiro flight in the United States at Willow Grove , Pennsylvania on December 18 , 1928 . The C.8W is the oldest autogiro in the USA . As of 2007 , two examples are extant : Weir 's machine preserved at the Musée de l'Air et de l'Espace in Paris , and Pitcairn 's at the National Air and Space Museum in Washington DC.  - Avro was a British aircraft manufacturer founded in 1910 whose designs include the Avro 504 used as a trainer in the First World War, the Avro Lancaster, one of the pre-eminent bombers of the Second World War, and the delta wing Avro Vulcan, a stalwart of the Cold War.  - Croydon is a large town in south London, England, the principal settlement of the London Borough of Croydon. It is located south of Charing Cross. It is one of the largest commercial districts outside of Central London, bearing one of the largest shopping districts and a developed night-time economy. It is identified in the London Plan as one of 11 metropolitan centres in Greater London. It has a population of 52,104 in the 2011 census, comprising the Addiscombe, Broad Green and Fairfield wards.  - A biplane is a fixed-wing aircraft with two main wings stacked one above the other. The first powered, controlled aeroplane to fly, the Wright Flyer, used a biplane wing arrangement, as did many aircraft in the early years of aviation. While a biplane wing structure has a structural advantage over a monoplane, it produces more drag than a similar unbraced or cantilever monoplane wing. Improved structural techniques, better materials and the quest for greater speed made the biplane configuration obsolete for most purposes by the late 1930s.  - The Avro Vulcan (later Hawker Siddeley Vulcan from July 1963) is a jet-powered tailless delta wing high-altitude strategic bomber, which was operated by the Royal Air Force (RAF) from 1956 until 1984. Aircraft manufacturer A.V. Roe and Company (Avro) designed the Vulcan in response to Specification B.35/46. Of the three V bombers produced, the Vulcan was considered the most technically advanced and hence the riskiest option. Several scale aircraft, designated Avro 707, were produced to test and refine the delta wing design principles.  - The Avro 504 was a World War I biplane aircraft made by the Avro aircraft company and under licence by others. Production during the War totalled 8,970 and continued for almost 20 years, making it the most-produced aircraft of any kind that served in World War I, in any military capacity, during that conflict. Over 10,000 were built from 1913 to the time production ended in 1932.    After reading the paragraphs above, we are interested in knowing the entity with which 'cierva c.8' exhibits the relationship of 'subclass of'. Find the answer from the choices below.  Choices: - air force  - aircraft  - application  - attempt  - autogyro  - biplane  - bomber  - borough  - c  - census  - combat  - combat aircraft  - configuration  - count  - cross  - delta  - derivative  - design  - doctrine  - engine  - engineer  - england  - english  - force  - heavy bomber  - helicopter  - invention  - language  - light  - person  - planning  - policy  - production  - prototype  - public  - rotation  - rotor  - satellite  - sea  - second  - single  - spanish  - specification  - speed  - structure  - test  - time  - town  - war  - wing  - world
Answer:
autogyro