Q:Information:  - A traction motor is an electric motor used for propulsion of a vehicle, such as an electric locomotive or electric roadway vehicle.   - The Hamburg S-Bahn is rapid mass transit railway network in the Hamburg Metropolitan Region. Together, the S-Bahn, the Hamburg U-Bahn, the AKN railway and the regional railway form the backbone of railway public transport in the city and the surrounding area. The network has operated since 1907 as an electric rapid transit system, under the direction of the state railway, and is member of Hamburger Verkehrsverbund (HVV), "Hamburg's transport association". There are six lines, serving 68 stations, on of route. On an average working day the S-Bahn transports about 590,000 passengers; in 2010 about 221 million people used the S-Bahn.  - An electric multiple unit or EMU is a multiple unit train consisting of self-propelled carriages, using electricity as the motive power. An EMU requires no separate locomotive, as electric traction motors are incorporated within one or a number of the carriages. Most EMUs are used for passenger trains, but some have been built or converted for specialised non-passenger roles, such as carrying mail or luggage, or in departmental use, for example as de-icing trains. An EMU is usually formed of two or more semi-permanently coupled carriages, but electrically powered single-unit railcars are also generally classed as EMUs.  - Low German or Low Saxon ( or in the wider sense) is a West Germanic language spoken mainly in northern Germany and the eastern part of the Netherlands. It is descended from Old Saxon in its earliest form.  - A train is a form of rail transport consisting of a series of vehicles that usually runs along a rail track to transport cargo or passengers. Motive power is provided by a separate locomotive or individual motors in self-propelled multiple units. Although historically steam propulsion dominated, the most common modern forms are diesel and electric locomotives, the latter supplied by overhead wires or additional rails. Other energy sources include horses, engine or water-driven rope or wire winch, gravity, pneumatics, batteries, and gas turbines. Train tracks usually consist of two running rails, sometimes supplemented by additional rails such as electric conducting rails and rack rails, with a limited number of monorails and maglev guideways in the mix. The word 'train' comes from the Old French "trahiner", from the Latin "trahere" 'pull, draw'.  - A railcar, in British English and Australian English, is a self-propelled railway vehicle designed to transport passengers. The term "railcar" is usually used in reference to a train consisting of a single coach (carriage, car), with a driver's cab at one or both ends. Some railways, e.g., the Great Western Railway, used the term Railmotor. If it is able to pull a full train, it is rather called a motor coach or a motor car.  - The DRG Class ET 171 ( since 1968 DB Class 471/871 ) is a three - car electric multiple unit train built for the Hamburg S - Bahn .  - The Hamburg U-Bahn is a rapid transit system serving the cities of Hamburg, Norderstedt and Ahrensburg in Germany. Although technically an underground, most of the system's track length is above ground. The network is interconnected with the city's S-Bahn system, which also has underground sections. It is operated by Hamburger Hochbahn within the Hamburger Verkehrsverbund (HVV). It was opened in February 1912, and comprises four lines serving 91 stations, with a route length of in 2012.  - The Hamburger Verkehrsverbund (HVV) is a company coordinating public transport in and around Hamburg, Germany. Its main objectives are to provide a unified fare system, requiring only a single ticket for journeys with transfers between different operating companies, and to facilitate and speed up travel by harmonising the individual companies' schedules. At its inception in 1965, HVV was the first organisation of this kind worldwide.  - The Metropolregion Hamburg (German for Hamburg Metropolitan Region) is the compilation of eight districts in the German federal state of Lower Saxony, six districts in Schleswig-Holstein, two districts in Mecklenburg-Vorpommern and the city-state of Hamburg in northern Germany. It covers an area of ca , and is home to more than 5.1 million inhabitants.  - A locomotive or engine is a rail transport vehicle that provides the motive power for a train. The word originates from the Latin "loco"  "from a place", ablative of "locus", "place" + Medieval Latin "motivus", "causing motion", and is a shortened form of the term "locomotive engine", first used in the early 19th century to distinguish between mobile and stationary steam engines.  - The Elbe (; Low German: "Elv") is one of the major rivers of Central Europe. It rises in the Krkonoše Mountains of the northern Czech Republic before traversing much of Bohemia (Czech Republic), then Germany and flowing into the North Sea at Cuxhaven, northwest of Hamburg. Its total length is .  - The European Union (EU) is a political and economic union of member states that are located primarily in Europe. It has an area of , and an estimated population of over 510 million. The EU has developed an internal single market through a standardised system of laws that apply in all member states. EU policies aim to ensure the free movement of people, goods, services, and capital within the internal market, enact legislation in justice and home affairs, and maintain common policies on trade, agriculture, fisheries, and regional development. Within the Schengen Area, passport controls have been abolished. A monetary union was established in 1999 and came into full force in 2002, and is composed of 19 EU member states which use the euro currency.  - Electricity is a physical phenomenon associated with the presence of electric charge. Although initially considered a phenomenon separate to magnetism, since the development of Maxwell's Equations both are recognized as part of a single phenomenon:electromagnetism. Various common phenomena are related to electricity, including lightning, static electricity, electric heating, electric discharges and many others. In addition, electricity is at the heart of many modern technologies.  - Hamburg (local pronunciation ; Low German/Low Saxon: "Hamborg" ), officially "Freie und Hansestadt Hamburg" (Free and Hanseatic City of Hamburg), is the second largest city in Germany and the eighth largest city in the European Union. It is the second smallest German state by area. Its population is over 1.7 million people, and the wider Hamburg Metropolitan Region covers more than 5.1 million inhabitants. The city is situated on the river Elbe.  - Germany, officially the Federal Republic of Germany, is a federal parliamentary republic in central-western Europe. It includes 16 constituent states, covers an area of , and has a largely temperate seasonal climate. With about 82 million inhabitants, Germany is the most populous member state of the European Union. After the United States, it is the second most popular immigration destination in the world. Germany's capital and largest metropolis is Berlin. Other major cities include Hamburg, Munich, Cologne, Frankfurt, Stuttgart and Düsseldorf.  - Multiple units (MU) are self-propelled train carriages capable of coupling with other units of the same or similar type and still being controlled from one driving cab. Often these are passenger trainsets consisting of more than one carriage. Single self-propelling carriages (also called railcars, rail motor coaches or railbuses) are multiple units if capable of operating with other units.    After reading the paragraphs above, we are interested in knowing the entity with which 'drg class et 171' exhibits the relationship of 'subclass of'. Find the answer from the choices below.  Choices: - being  - british english  - city  - climate  - coach  - company  - day  - driving  - electric charge  - electric motor  - electric multiple unit  - electricity  - energy  - federal republic  - gas  - german  - germany  - heart  - heating  - latin  - length  - lightning  - locomotive  - low german  - market  - mass  - member  - member state  - mu  - network  - parliamentary republic  - phenomenon  - physical phenomenon  - population  - power  - public  - public transport  - rail  - railcar  - rapid transit  - reference  - republic  - rope  - running  - series  - single  - speed  - system  - term  - track  - trade  - train  - transport  - type  - vehicle
A:
locomotive