Question: which airline maintains hubs at Berlin Tegel Airport and Düsseldorf Airport and continues to work with Kosovo Airlines?
Context: Düsseldorf Airport Terminal ("Düsseldorf Flughafen Terminal") is an underground station on the Rhine-Ruhr S-Bahn at the end of the Düsseldorf-Unterrath–Düsseldorf Airport Terminal railway, situated underneath Terminal C of Düsseldorf Airport, Düsseldorf in western Germany.  It is served by the S11 line. Germanwings GmbH is a German low-cost airline based in Cologne and a wholly owned subsidiary of Lufthansa.  Its main hubs are Cologne Bonn Airport, Stuttgart Airport, Hamburg Airport, Berlin Tegel Airport and Düsseldorf Airport; further bases are Hannover Airport and Dortmund Airport. Kosova Airlines is an airline that is based in Kosovo .  The airline links Pristina to major European cities.  The airline was established in autumn 2003 by the United Nations Interim Administration Mission in Kosovo (UNMIK) and the Kosovo Government.  On 10 May 2006, the only aircraft in the Kosova Airlines fleet, a Boeing 737-700, which was wet leased from the German airline Hamburg International, was returned to that airline, and Kosova Airlines ceased operating flights.  The airline however continues to work with other airline companies flying into Pristina, such as Germanwings, LTU, Air Berlin and a few others. Air Berlin PLC & Co.  Luftverkehrs KG (), branded as airberlin or airberlin.com, is Germany's second-largest airline, after Lufthansa, and Europe's seventh-largest airline in terms of passengers carried.  It maintains hubs at Berlin Tegel Airport and Düsseldorf Airport and serves 12 German cities as well as destinations in Europe, the Caribbean and the Americas. Berlin Schönefeld Airport ("   ") (IATA: SXF, ICAO: EDDB) is the secondary international airport of Berlin, the capital of Germany.  It is located 18 km southeast of Berlin near the town of Schönefeld in the state of Brandenburg and borders Berlin's southern boundary.  It is the smaller of the two airports in Berlin, after Berlin Tegel Airport, and is a base for Condor, easyJet and Ryanair. Modern Air Transport, Inc. (originally Modern Air Transport/MAT, subsequently Modern Air) was a United States-based non-scheduled and supplemental carrier founded in 1946.  At different stages in its history its operations were based in Newark and Trenton, New Jersey, Baltimore, and Miami.  In addition to Miami, New York used to be a base for Modern Air.  In 1968, the airline established an overseas base at Berlin Tegel Airport in what used to be West Berlin prior to German reunification.  Between 1968 and 1974, operations increasingly focused on Berlin Tegel.  Modern Air ceased trading in 1975. Eurowings GmbH is a German airline headquartered in Düsseldorf and a fully owned subsidiary of the Lufthansa Group.  It serves a network of domestic and European destinations as well as some long-haul routes and maintains bases at Berlin Tegel Airport, Cologne Bonn Airport, Düsseldorf Airport, Hamburg Airport, and Vienna International Airport. Aeroamerica, Inc. was founded as a US supplemental carrier in 1973.  It was headquartered at Seattle Boeing Field, Washington.  In 1975 the airline established an overseas base at Tegel Airport in what used to be West Berlin prior to German reunification.  Berlin Tegel was the main operating base from 1975 until 1979.  Aeroamerica ceased operations in 1982. Berlin Brandenburg Airport (IATA: BER, ICAO: EDDB) (German: "Flughafen Berlin Brandenburg Willy Brandt" ) is an international airport under construction, located adjacent to the current Berlin Schönefeld Airport in Schönefeld, 18 km south of the city centre of Berlin, the capital of Germany.  It was originally intended to replace both Schönefeld and Berlin Tegel Airport, and to become the single commercial airport serving Berlin and the surrounding state of Brandenburg, an area with a combined 6 million inhabitants.  However, it is now planned that it will only replace Tegel, and the old Schönefeld airport is currently being expanded because it will still be required to cope with rising passenger numbers. Flughafen Berlin Brandenburg GmbH, commonly abbreviated FBB, is a German airport operator.  Currently, it operates Berlin Tegel Airport and Berlin Schönefeld Airport, and is the building owner and future operator of Berlin Brandenburg Airport.
Answer: Air Berlin