Westlake is a light rail and bus station located that is part of the Downtown Seattle Transit Tunnel in Seattle, Washington.
 The station serves Pine Street between 3rd and 6th avenues in Downtown Seattle, near Westlake Center and Westlake Park.
 It is served by the Central Link, part of Sound Transit's Link light rail system, as well as buses from King County Metro and Sound Transit Express.
 The station is also connected above ground by buses, the South Lake Union Streetcar, and the Seattle Center Monorail.
Beacon Hill tunnel is a public transit tunnel in Seattle, Washington, carrying the Central Link light rail line under Seattle's Beacon Hill between Rainier Valley and SoDo just east of Interstate 5.
 The Beacon Hill Link Light Rail station is approximately 165 ft underground near the midpoint of the tunnel.
The Link light rail is a rapid transit rail system in the Seattle metropolitan area of Washington State, being designed, built and operated by the region's mass transportation agency, Sound Transit.
 Currently the system consists of two separate lines: Tacoma Link, a streetcar line operating in downtown Tacoma and Central Link, a light rail line operating between the University of Washington in Seattle and the Angle Lake station in SeaTac, Washington.
 Extensions are being planned or constructed that will bring light rail north to Lynnwood and Everett, east to Redmond and south to Kent, Des Moines, Federal Way, and the Tacoma Dome.
 Additional lines are planned to service Ballard, West Seattle, Issaquah and south Kirkland.
Central Link is a light rail line in Seattle, Washington, part of Sound Transit's Link light rail system.
 It serves 16 stations in the cities of Seattle, SeaTac, and Tukwila, traveling 20 mi between and .
 The line connects the University District, Downtown Seattle, the Rainier Valley, and Seattle–Tacoma International Airport.
 Central Link carried over 19 million total passengers in 2016, averaging 59,000 daily passengers on weekdays.
 It runs for 20 hours per day on weekdays and Saturdays, with headways of up to six minutes during peak hours, and reduced 18-hour service on Sundays and holidays.
 Trains are composed of two or more cars that can carry 194 passengers, including 74 in seats, along with wheelchairs and bicycles.
Mount Baker is a light rail station located in Seattle, Washington.
 It is situated between the Columbia City and Beacon Hill stations on the Central Link line, which runs from Seattle–Tacoma International Airport to Downtown Seattle and the University of Washington as part of the Link Light Rail system.
 The elevated station consists of two side platforms located west of the intersection of Rainier Avenue and Martin Luther King Jr.
 Way in the Mount Baker neighborhood, part of Seattle's Rainier Valley.
Seattle–Tacoma International Airport (IATA: SEA, ICAO: KSEA, FAA LID: SEA) , also referred to as Sea–Tac Airport or Sea–Tac ( ), is the primary commercial airport serving the Seattle metropolitan area in the U.S. state of Washington.
 It is located in the city of SeaTac, approximately 13 mi south of Downtown Seattle.
 The airport, the largest in the Pacific Northwest region of North America, is owned and operated by the Port of Seattle.
The University Link tunnel is a 3.15 mi light rail tunnel in Seattle, Washington.
 The twin-bore tunnel carries Link Light Rail service on the University Link Extension of Central Link, running from the Downtown Seattle Transit Tunnel to University of Washington station via Capitol Hill station.
 The 21 ft tunnels are lined with precast gasketed concrete segments connected with steel bolts and was excavated using three tunnel-boring machines in 2011 and 2012.
 Light rail service began on March 19, 2016.
The Downtown Seattle Transit Tunnel (DSTT), also referred to as the Metro Bus Tunnel, is a 1.3 mi pair of public transit tunnels in Seattle, Washington, United States.
 The tunnel serves Downtown Seattle, running west under Pine Street from 9th Avenue to 3rd Avenue, and south under 3rd Avenue to South Jackson Street.
 It was used only by buses from its opening in 1990 until 2005, and since 2009 it has been shared by buses and light rail.
 The double-track tunnel and its stations, except Convention Place, constitute parts of the Central Link light rail line, which continues north to the University of Washington station and south through the Rainier Valley to Seattle–Tacoma International Airport as part of Sound Transit's Link light rail network.
 Its five stations are also served by King County Metro and Sound Transit Express buses that leave the tunnel north via Interstate 5, south via the SODO Busway, or east via Interstate 90.
 The DSTT is the busiest section of the Link light rail network, with an average of over 10,000 weekday boardings.
 It is owned by King County Metro and shared with Sound Transit through a joint-operating agreement signed in 2002.
 The Downtown Seattle Transit Tunnel is one of two tunnels in the United States shared by buses and trains, the other being the Mount Washington Transit Tunnel in Pittsburgh, and is the only one in the United States with shared stations.
Rainier Beach is a light rail station located in Seattle, Washington.
 It is situated between the Tukwila International Boulevard and Othello stations on the Central Link line.
 The line runs from Seattle–Tacoma International Airport to Downtown Seattle and the University of Washington as part of the Link light rail system.
 The station consists of an at-grade island platform south of South Henderson Street in the median of Martin Luther King Jr.
 Way in the Rainier Beach neighborhood, part of Seattle's Rainier Valley.
Columbia City is a light rail station located in Seattle, Washington.
 It is situated between the Othello and Mount Baker stations on the Central Link line, which runs from Seattle–Tacoma International Airport to Downtown Seattle and the University of Washington as part of the Link light rail system.
 The station consists of two at-grade side platforms between South Alaska Street and South Edmunds Street in the median of Martin Luther King Jr.
 Way South in the Columbia City neighborhood, part of Seattle's Rainier Valley.

Question: What is the primary Seattle airport that is connected to the Central Link light rail?
Answer: Seattle–Tacoma International Airport