Question: Which of the following airports is closer to the city center of Beijing City: Beijing Xijiao Airport or Beijing Capital International Airport? 
Context: China Eastern Airlines Corporation Limited (, colloquially known as 东航/東航) is an airline headquartered in the China Eastern Airlines Building, on the grounds of Shanghai Hongqiao International Airport in Changning District, Shanghai, China.  It is a major Chinese airline operating international, domestic and regional routes.  Its main hubs are at Shanghai Pudong International Airport and Shanghai Hongqiao International Airport, with secondary hubs at Beijing Capital International Airport, Kunming Changshui International Airport and Xi'an Xianyang International Airport. Ai Weiwei (,    ; born 28 August 1957 in Beijing) is a Chinese contemporary artist and activist.  His father's (Ai Qing) original surname was written Jiang ().  Ai collaborated with Swiss architects Herzog & de Meuron as the artistic consultant on the Beijing National Stadium for the 2008 Olympics.  As a political activist, he has been highly and openly critical of the Chinese Government's stance on democracy and human rights.  He has investigated government corruption and cover-ups, in particular the Sichuan schools corruption scandal following the collapse of so-called "tofu-dreg schools" in the 2008 Sichuan earthquake.  In 2011, following his arrest at Beijing Capital International Airport on 3 April, he was held for 81 days without any official charges being filed; officials alluded to their allegations of "economic crimes". Beijing Capital International Airport (IATA: PEK, ICAO: ZBAA) is the main international airport serving Beijing.  It is located 32 km northeast of Beijing's city center, in an enclave of Chaoyang District and the surroundings of that enclave in suburban Shunyi District.  The airport is owned and operated by the Beijing Capital International Airport Company Limited, a state-controlled company.  The airport's IATA Airport code, PEK, is based on the city's former romanized name, Peking. Beijing Capital International Airport Co., Ltd. (BCIA), majority owned by Capital Airport Holding, is engaged in the ownership and operation of the Beijing Capital International Airport in Beijing, China and the provision of related services. The Northern Airport Line, officially numbered S28, is an 11.29 km toll road extension that runs from G45 Daqing–Guangzhou Expressway (formerly Beijing-Chengde Expressway) to the Beijing Capital International Airport in Beijing, China.  It was opened in September 2006.  The opening of this road has helped to alleviate traffic on the Airport Expressway, which had been the sole highway link to the airport.  The Northern Airport Line allows drivers from Zhongguancun and points north and west of the city to head north first on Jingcheng Expressway before going directly east to the airport, instead of having to go east on the 4th Ring Road to get on the Airport Expressway, where traffic is often clogged near the Siyuan Bridge. Beijing Xijiao Airport (ICAO: ZBBB) is a military airport in Beijing, China.  It was also used by charter flights.  It is located in Haidian District, 19.75 miles from Beijing Capital International Airport and about 8 miles from the city centre.  It has one runway numbered 18/36. The Beijing Airport Shuttle Bus (北京首都机场巴士) is an express public bus service mainly between the Beijing Capital International Airport (Capital Airport) and points within the city of Beijing and the surrounding region.  As of March 2013, there were eleven airport shuttle bus routes from the Capital Airport and the city proper, and six routes to Tianjin and Hebei Province.  In addition, the Beijing Airport Shuttle Bus also runs one route from Xidan in the city to the Beijing Nanyuan Airport.  One way fare on routes to the city is ¥16 (¥24 to Beijing South Station as of April 2015) and varies from ¥40 to ¥140 on routes to Tianjin and cities in Hebei. The Airport Express line of the Beijing Subway (), also known by the initials ABC, which stands for Airport Beijing City, is a rapid transit line that provides an airport rail link service from Beijing city center to the Beijing Capital International Airport.  The line became operational on July 19, 2008, in time to serve the 2008 Summer Olympic Games.  On subway maps, the Airport Express' color is      magnolia. China Aviation Oil (Singapore) Corporation Ltd ("CAO") () is the largest purchaser of jet fuel in the Asia Pacific region and the key supplier of imported jet fuel to the civil aviation industry of the People's Republic of China ("PRC").  CAO supplies to the three key international airport in the PRC, i.e. Beijing Capital International Airport, Shanghai Pudong International Airport and Guangzhou Baiyun International Airport, and accounts for more than 90% of PRC's jet fuel imports.  CAO also engages in international trading of jet fuel and other oil products.  CAO owns investments in strategic oil-related businesses, which include Shanghai Pudong International Airport Aviation Fuel Supply Company Ltd and China National Aviation Fuel TSN-PEK Pipeline Transportation Corporation Ltd. This is a list of busiest airports in Asia, ranked by total passengers per year, which includes arrival, departure and transit passengers.  Beijing Capital International Airport has been the busiest airport in Asia since 2009.  The tables also shows the percentage change in total passenger traffic over last year.  Asian airports are those that are located in the 48 countries and 6 dependent states as defined by UN and fall within the Asian region.  Airports in Moscow and Istanbul airport are located in the European part of their respective countries and so are not included in this list.  While Turkey is a member state of The Council of Europe which includes Turkish airspace within Europe and hence traffic of Turkish airports, even those falling in the Asian region, are included in the busiest airport in Europe list.
Answer: Beijing Xijiao Airport