Question: The Ford Explorer and the Mercury Mountaineer are very similar vehicles. What year did the Ford Explorer start being produced?

full_context: Document 1: Ford Taurus (sixth generation): The sixth generation of the Ford Taurus is a full-size car manufactured by Ford. Produced since June 2009, it is the current version of the Ford Taurus in markets outside of China. Sharing its underpinnings with its 2008-2009 predecessor, the sixth generation features a completely redesigned exterior and interior, marking the introduction of Kinetic Design for the Taurus.
Document 2: Saleen XP8: The Saleen XP8 is a performance sport utility vehicle based on the Ford Explorer created by Saleen during the years 1998-2001. There were three prototype models, based on the 1997 Explorer XLT, which when viewed closely, has distinct characteristics apart from the production models (rear hatch design, taillights, and integrated license plate into the rear bumper). The Saleen XP8 comes in two wheel drive, or all wheel drive four-door configurations, packing either a 5.0-liter V-8, or a Saleen-developed supercharged 5.0-liter/286-horsepower V-8.
Document 3: Ford Fusion (Americas): The Ford Fusion is a four-door, five passenger mid-size sedan manufactured and marketed by Ford across three generations in gasoline and gas/electric hybrid variants. Introduced for model year 2006, the Fusion is manufactured at Ford's Hermosillo Stamping & Assembly plant along with its rebadged variant the Lincoln MKZ — and formerly with its now discontinued rebadged variant, the Mercury Milan, all sharing the CD3 platform. The Ford Fusion mainly competes against cars such as the Buick Regal, Chevrolet Malibu, Honda Accord, Hyundai Sonata, Kia Optima, Mitsubishi Lancer, Nissan Altima, Toyota Camry and Volkswagen Passat.
Document 4: Ford 6R transmission: The 6R is a six-speed automatic transmission for longitudinal engine placement in rear-wheel drive vehicles. It is based on the ZF 6HP26 transmission and is built under license by the Ford Motor Company at its Livonia Transmission plant in Livonia, Michigan. The 6R debuted in 2005 in the 2006 model year Ford Explorer and Mercury Mountaineer.
Document 5: Ford Explorer Sport Trac: The Ford Explorer Sport Trac, sometimes referred to as simply the Ford Sport Trac, is a mid-size pickup truck sold mostly in North America produced by Ford from 2000 through 2010. The Sport Trac was based on the Ford Explorer SUV - not based on the compact Ford Ranger (North America) - because it was introduced when the Explorer and Ranger platforms diverged (Explorer's chassis was a heavy duty variant of the Ranger's). The Sport Trac fell between the Ranger and Ford F-Series in Ford's truck lineup, based on capability and price. It competed with other mid-size trucks and SUVs, such as the mid-size Honda Ridgeline and even the larger full-size Chevrolet Avalanche. During its first year on sale in the U.S., there was a waiting list of over 3 months. The Sport Trac was a Class 2 vehicle with a GVWR of 6250 lbs. and a maximum GCWR of 12,000 lbs. This made it one of the more and the then most capable mid-size pickups, having a greater GVWR and GCWR than the Dodge Dakota, GM's GMC Canyon/Chevrolet Colorado pickups and Toyota Tacoma.
Document 6: Ford Taurus: The Ford Taurus is an automobile manufactured by Ford in the United States. Now in its sixth generation, it was originally introduced in the 1986 model year, and has remained in near-continuous production for more than two decades. It has had a Mercury-branded twin, the Sable (1986–2005; 2008–2009), as well as a performance variant, the Ford Taurus SHO (1989–1999 and 2010–); in addition, it served as the basis for the first-ever front-wheel drive Lincoln Continental (1988–2002). It was a front-wheel drive mid-size car until 2007, and has been a "global" full-size car (built on the Ford D3 platform) since 2008, and available in front- or all-wheel drive since 2008.
Document 7: Ford Explorer: The Ford Explorer is a full-size sport utility vehicle produced by the American manufacturer Ford Motor Company since 1990, based since 2010 on a crossover platform. The Ford Explorer became one of the most popular sport utility vehicles on the road. The model years 1991 through 2010 were traditional body-on-frame, mid-size SUVs. For the 2011 model year, Ford moved the Explorer to a more modern unibody, full-size crossover SUV platform, the same Volvo-derived platform the Ford Flex and Ford Taurus use although with significantly greater ground clearance. It is slotted between the traditional body-on-frame, full-size Ford Expedition and the mid-size CUV (Crossover Utility Vehicle) Ford Edge. Although outwardly similar, the fifth generation Explorer, Ford Edge and Ford Escape do not share platforms. The fifth generation Explorer does, however, share platforms with the Ford Flex and Lincoln MKT.
Document 8: Ford E-Series: The Ford E-Series (also known as the Ford Econoline and Ford Club Wagon throughout various stages of its production) is a range of full-size vans produced by Ford Motor Company. Introduced for the 1961 model year as the replacement for the Ford F-Series panel van, four generations of the model line have been produced. In addition to cargo van and passenger van body styles, the Ford E-Series has been produced as a cutaway van chassis and stripped chassis (a chassis without bodywork).
Document 9: Ford F-Series (sixth generation): The sixth generation of the Ford F-Series is a line of pickup trucks and medium-duty commercial trucks that were produced by Ford from 1972 to 1979. This generation was launched in December 1972 for the 1973 model year. These were the last generation of trucks to use the F-Series chassis introduced in 1965. After a decade as a compact SUV, the Bronco was redesigned as a shortened version of the F-Series. This generation also marks the introduction of the F-150, which today is the most popular model.
Document 10: Mercury Lynx: The Mercury Lynx is a compact car that was produced by Mercury for model years 1981 to 1987. It was a rebadged version of the Ford Escort. In 1987, the Lynx was dropped after slumping sales (although at one point, it was Mercury's best-selling car). In 1988, Mercury launched the Tracer as the Lynx's replacement. The Tracer was based on the Mazda 323, was built in Mexico and Japan (depending on model), and shared nothing with the Lynx.
Document 11: Mercury Tracer: The Mercury Tracer is a compact car that was marketed by Mercury from 1987 for the 1988 model year until 1999. The replacement for the Ford Escort-derived Lynx, the first generation of the Tracer was a modified version of the Asia-Pacific market Ford Laser, itself a variant of the Mazda 323. In 1990 for the 1991 model year, the Tracer became the Mercury counterpart of the Ford Escort in North America. All three generations of the Tracer were based on variations of the Mazda 323/Protegé.
Document 12: Ford Explorer Fuel Cell Prototype: Ford Explorer Fuel Cell Prototype is a hydrogen car based on the standard Ford Explorer. The car was introduced at the 2007 Greater Los Angeles Auto Show, which was held in November 2006.
Document 13: Mercury Mountaineer: The Mercury Mountaineer was a mid-size luxury sport utility vehicle (SUV) that was sold by Mercury from 1997 until 2010. Sharing many of its features with the Ford Explorer, the vehicles were virtually identical in terms of hardware. Externally, they were styled somewhat differently, and the Mountaineer was positioned with a more upscale interior, with the Mountaineer's MSRP coming in at $1,000–$6,000 more than the Explorer. It was last redesigned for the 2006 model year with a new frame, looking very similar to its previous model.
Document 14: Lincoln Aviator: The Lincoln Aviator is a mid-size luxury sport-utility vehicle (SUV) that was sold by the Lincoln division of Ford Motor Company from model years 2003 to 2005 in North America. A rebadged variant of the Mercury Mountaineer and Ford Explorer four-door SUVs, the Aviator was the shortest Lincoln vehicle ever sold (at its debut).
Document 15: Hyundai Santa Fe: The Hyundai Santa Fe (Korean: 현대 싼타페 ) is a sport utility vehicle (SUV) produced by the South Korean manufacturer Hyundai since 2000. It is named after the city of Santa Fe, New Mexico, and was introduced for the 2001 model year as Hyundai's first SUV, released at the same time as the Ford Escape and Pontiac Aztek. The Santa Fe was a milestone in the company's restructuring program of the late 1990s because, despite receiving criticism from journalists for its obscure looks, the SUV was a hit with American buyers. The SUV was so popular that at times, Hyundai had trouble supplying the demand. The Santa Fe quickly became Hyundai's best seller and contributed to Hyundai's success in the United States. As of 2007, the Santa Fe falls between the slightly smaller compact crossover Tucson and the larger, yet related luxury crossover SUV Veracruz (which replaced the Terracan).
ground_truth: 1990