Question: Hilton Head Airport and San Francisco International Airport, are located in which country?
Context: United p.s. is a premium service offered by United Airlines on flights between Newark Liberty International Airport and Los Angeles International Airport and San Francisco International Airport, as well as between Boston Logan International Airport and San Francisco International Airport.  The fleet consists of specially configured Boeing 757-200 aircraft with three classes of service: United Business, United Economy Plus, and United Economy.  Each class of service includes certain amenities not offered on regular flights. Hilton Head Airport (IATA: HHH, ICAO: KHXD, FAA LID: HXD) is a public use airport located on Hilton Head Island, in Beaufort County, South Carolina, United States.  Also known as Hilton Head Island Airport, it is owned by Beaufort County.  Mostly used for general aviation, it is also served by a commercial airline and one public charter airline operating limited service.  It is the only airport on Hilton Head Island. Hilton Head Preparatory School (HHP) is a private school for grades Junior Kindergarten through 12th grade, located in Hilton Head Island, South Carolina.  It belongs to the South Carolina Independent School Association.  The school is accredited by the Southern Association of Colleges and Schools and the Southern Association of Independent Schools.  It is the only school on Hilton Head Island to be accredited by the National Association of Independent Schools.  Its enrollment for the 2006-2007 school year was 450 students.  Over fifty percent of the faculty hold advanced degrees in their subject area. Stol Air Commuter was a United States commuter airline that began service around 1974.  The air carrier was also known as STOL Air Commuter thus reflecting its use of STOL (short take off and landing) aircraft.  It served the San Francisco, California Bay Area and northern California.  The airline was based in San Rafael in Marin County just north of the city of San Francisco and also had administrative offices located in Santa Rosa, CA at one point.  Stol Air Commuter operated scheduled passenger air service connecting several cities in the San Francisco Bay Area as well as northern California with San Francisco International Airport (SFO).  According to the airline's system timetable, in the spring of 1975 Stol Air Commuter was operating 66 daily flights serving SFO via United Airlines gate 10 at the airport. Northern California TRACON (NCT) (Terminal Radar Approach Control), or NorCal TRACON for short, is an air traffic control facility that provides safety alerts, separation, and sequencing of air traffic arriving, departing, and transiting the airspace and airports in Northern California.  Located in Rancho Cordova near Sacramento, NCT controls airspace over 19000 square miles, and serves Reno International Airport, Sacramento International Airport, San Jose International Airport, Oakland International Airport, and San Francisco International Airport, plus 19 other smaller airports with air traffic control towers.  NCT is the 3rd busiest TRACON in America.  NorCal TRACON is the step between local control (in an airport's control tower) and Air Route Traffic Control Center (ARTCC), in this case, Oakland Center (ICAO code: ZOA).  San Francisco International Airport is the 2nd largest airport in California and the largest airport serving Northern California. The San Francisco Fire Department (SFFD) provides fire and emergency medical services to the City and County of San Francisco, California.  The San Francisco Fire Department, along with the San Francisco Police Department and San Francisco Sheriff's Department, serves an estimated population of 1.4 million people, which includes the approximately 850,000 citizens residing in the 47.5 sqmi of San Francisco (including Treasure Island, Yerba Buena Island, San Francisco-Oakland Bay Bridge, Golden Gate Bridge, Alcatraz Island, the San Francisco International Airport, and the Presidio of San Francisco/Golden Gate National Recreation Area. Hilton Head Island High School (shortened to Hilton Head High, HHIHS, or HHH) is a public high school within the Beaufort County School District, located in Hilton Head Island, South Carolina, United States.  The high school serves students on the island in addition to some students living in Bluffton.  The school served 1,161 students in the 2011–2012 school year.  The school has had a long-standing relationship with the International Baccalaureate Programme. San Francisco International Airport station is a Bay Area Rapid Transit (BART) reversal station on the Pittsburg/Bay Point–SFO/Millbrae line located inside the San Francisco International Airport, also known as SFO or SFIA. Savannah/Hilton Head International Airport (IATA: SAV, ICAO: KSAV, FAA LID: SAV) is a public and military use airport owned by the City of Savannah and managed by the Savannah Airport Commission.  The airport is located seven nautical miles (8 mi, 13 km) northwest of the central business district of Savannah, a city in Chatham County, Georgia, United States.  It had been known as Savannah International Airport, Travis Field and Chatham Field.  The airport is just off Interstate 95, between Savannah and the city of Pooler, Georgia.  It is the chief commercial airport for the three-county Savannah metropolitan area, although nearly 40 percent of the airport's total passenger traffic is bound for Hilton Head Island, South Carolina, located approximately 38.5 miles (approx. 42 minutes) away by car. San Francisco International Airport (IATA: SFO, ICAO: KSFO, FAA LID: SFO) is an international airport 13 mi south of downtown San Francisco, California, United States, near Millbrae and San Bruno in unincorporated San Mateo County.  It has flights to points throughout North America and is a major gateway to Europe and Asia.
Answer: United States