Question: The Volkswagen Concept D was envisioned by the chairman of the supervisory board until what date?

full_context: Document 1: Volvo Concept You: The Volvo Concept You is a concept car first revealed at the Frankfurt Motor Show in September 2011. The Concept You is an executive car with a 4-door fastback saloon-like styling and is a further development of the "Volvo Concept Universe" which was revealed earlier the same year. The design builds upon Scandinavian Design where simplicity, elegance and intuitively are key ingredients. Volvo has interpreted this to design the car around the driver and passengers in the car, hence the name "You". This includes, for example, that all buttons and knobs have been removed and replaced by easy-to-use touch-screen to control the features of the car. The exterior design is inspired by the classical Volvo models PV544 and the Amazon.
Document 2: Niki Lauda: Andreas Nikolaus "Niki" Lauda (born 22 February 1949) is an Austrian former Formula One driver and a three-time F1 World Drivers' Champion, winning in 1975, 1977 and 1984. He is currently the only driver to have been champion for both Ferrari and McLaren, the sport's two most successful constructors. More recently an aviation entrepreneur, he has founded and run two airlines (Lauda Air and Niki). He is also Bombardier Business Aircraft brand ambassador. He was also a consultant for Scuderia Ferrari and team manager of the Jaguar Formula One racing team for two years. He is currently working as a pundit for German TV during Grand Prix weekends and acts as non-executive chairman of the Mercedes AMG Petronas F1 Team. Lauda owns 10% of the team.
Document 3: Red Bull RB9: The Red Bull RB9 is a racing car designed by Formula One racing team Infiniti Red Bull Racing. The car was driven throughout the 2013 Formula One season by (then) three-time World Drivers' Champion Sebastian Vettel and team-mate Mark Webber. Sebastian Vettel, in keeping with his tradition of naming his cars, named his RB9 "Hungry Heidi," after German model Heidi Klum. Vettel would ultimately claim the Drivers' Championship title, for the fourth consecutive season, at the Indian Grand Prix , after ten wins during the season. Vettel and Webber also brought the car to the last win and world titles for a V8 and a naturally aspirated engine powered F1 car, marking the end of the V8 and the naturally aspirated engine era of Formula One which began in 1989 when turbocharged engines were banned at that time.
Document 4: Ferdinand Piëch: Ferdinand Karl Piëch (born 17 April 1937) is an Austrian business magnate, engineer and executive who was the chairman of the supervisory board ("Aufsichtsratsvorsitzender") of Volkswagen Group until 25 April 2015.
Document 5: Porsche: Dr. Ing. h.c. F. Porsche AG, usually shortened to Porsche AG (] ), is a German automobile manufacturer specializing in high-performance sports cars, SUVs and sedans. Porsche AG is headquartered in Stuttgart, and is owned by Volkswagen AG, which is itself majority-owned by Porsche Automobil Holding SE. Porsche's current lineup includes the 718 Boxster/Cayman, 911, Panamera, Macan and Cayenne.
Document 6: Volkswagen Concept D: The Volkswagen Concept D is a concept luxury liftback envisioned by Ferdinand Piëch and unveiled by Volkswagen at the 1999 International Motor Show Germany. It featured V10 TDI diesel engine (230 kW/313 bhp at 4000 rpm., 750 Nm torque), 6-speed Tiptronic, 4Motion all-wheel drive, air suspension with adaptive damping, and Bi-Xenon headlamps.
Document 7: Ferdinand Zvonimir von Habsburg: Ferdinand Zvonimir Maria Balthus Keith Michael Otto Antal Bahnam Leonhard von Habsburg (born 21 June 1997 in Salzburg), is the eldest son of Karl von Habsburg, head of the House of Habsburg-Lorraine. Habsburg is a racing driver currently competing in the FIA European Formula 3 Championship.
Document 8: Giovanni Ferrero: Giovanni Ferrero (born 21 September 1964) is an Italian businessman. He assumed the leadership of the confectionery company Ferrero SpA after the death of his brother Pietro Ferrero in 2011. He has a net worth of $24.2 billion as of May 2016, according to Bloomberg.
Document 9: Volkswagen New Compact Coupé: The VW New Compact Coupé (short VW NCC) is a close-to-production concept car of the German car manufacturer Volkswagen. The car was presented on the NAIAS 2010 in Detroit. It is equipped with a hybrid-drive and is positioned between the VW Scirocco and the VW Passat CC. The average fuel consumption is just 4.2 liters per 100 kilometers; the emission value is 98 grams of CO2 per kilometer. In contrast, the driving values are a top speed of 227 km/h and a sprint time of 8.6 seconds from 0 to 100 km/h.
Document 10: Audi quattro concept: The Audi quattro concept is a concept car produced by Audi and presented at the Paris Motor Show in 2010. It commemorates the 30th anniversary of the original Audi Quattro and the Audi quattro four wheel drive system. Based on the Audi RS5, it features a modified 2.5L five-cylinder TFSI engine and the sixth generation of quattro transmission. It had been reported that Audi are considering a limited production model (200–500 cars) based on the quattro concept, but the project was shelved in 2012.
Document 11: Volkswagen CrossBlue: The Volkswagen CrossBlue is a concept diesel plug-in-hybrid mid-size crossover SUV, intended to sit in the VW SUV range, below the Volkswagen Touareg. The concept version of the car has six seats, but the production version that will be based on it will have a traditional seven-seat layout. It is meant to replace the slow selling Volkswagen Routan minivan, and is intended to be sold exclusively in the American and Canadian markets. However Volkswagen of Australia is currently trying to convince Volkswagen executives to have the concept appear in Australian Auto Shows. In the American and Canadian markets, its targeted competitors are the Toyota Highlander, Toyota 4Runner, Ford Explorer, and Honda Pilot. On July 14, 2014, Volkswagen announced that the CrossBlue will be built at its factory in Chattanooga, Tennessee.
Document 12: Luca Cordero di Montezemolo: Luca Cordero di Montezemolo (] ; born 31 August 1947) is an Italian businessman, former Chairman of Ferrari, and formerly Chairman of Fiat S.p.A. and President of Confindustria and FIEG. He comes from an aristocratic family from the region of Piedmont in Italy. He graduated with a degree in law from La Sapienza University in 1971. Afterward, he studied for a masters degree in international commercial law at Columbia University. He is one of the founders and former president of NTV, an Italian company which is Europe's first private open access operator of 300 km/h (186 mph) high-speed trains.
Document 13: Volkswagen Milano: The Volkswagen model VW Milano is a prototype of an electric taxi, which was presented at the Hanover Fair in April 2010. It is a van-type car with 3 doors, an 85 kW electric motor and a 45 kWh lithium-ion-battery. The market introduction is planned for the year 2013.
Document 14: Martin Winterkorn: Martin Winterkorn (born 24 May 1947) is the former chairman of the board of directors (CEO, "Vorstandsvorsitzender" in German) of Volkswagen AG, the parent company of the Volkswagen Group, and former chairman of the supervisory board of Audi and Porsche Automobil Holding SE.
Document 15: Volkswagen Concept BlueSport: The Volkswagen Concept BlueSport is a mid-engined roadster concept car produced by Volkswagen. It was introduced at the 2009 North American International Auto Show in Detroit. The Concept BlueSport follows on from a previous roadster concept car, the Volkswagen Concept R, shown at the 2003 Frankfurt Motor Show.
ground_truth: 25 April 2015