Question: Which former tennis player played for the United States, Iván Molina or Alex O'Brien?
Context: Thomas Emmrich (born 21 July 1953) is a former tennis player for East Germany.  Between 1970 and 1988, Emmrich won 47 German Democratic Republic (GDR) titles (16 singles and 31 in the doubles and mixed).  Unfortunately, he entered the tennis scene after the GDR had decided to promote only those sports which were relevant for the Olympics’ medals table.  Thus, he was barred from international competitions outside the Eastern bloc countries and had to keep the status as an amateur.  However, he gained some points at an ATP tournament in Sofia as GDR functionaries had not noticed that it had become part of the ATP tour.  After this tournament, the ATP ranked him number 482—the only entry of a GDR tennis player in the ATP rankings. Dimitar Kuzmanov (Bulgarian: Димитър Кузманов , ] ; nickname: Miko; born 28 July 1993) is a Bulgarian professional tennis player and the current No. 3 Bulgarian in the ATP singles ranking.  His highest singles ranking was No. 281 (8 February 2016), whilst his best doubles ranking was No. 445 (8 February 2016).  Kuzmanov is a player of Tennis Club Lokomotiv Plovdiv and is coached by former Bulgarian tennis player Stefan Rangelov and by Bulgaria Fed Cup team's former tennis player and present captain Dora Rangelova.  In 2011 he was invited to play for Bulgaria Davis Cup team. Maria Fernanda Barbato Alves (born 17 April 1983), also known as Nanda Alves, is a Brazilian tennis player.  She is currently coached by her father Carlos and former tennis player Thomaz Koch.  As of 1 March 2010, Alves is ranked World No. 262, and is the highest ranked Brazilian player.  She has enjoyed success at the ITF Circuit, winning 18 singles and 26 doubles titles so far.  Alves made her WTA Tour debut at Copa Colsanitas in 2004, and has played qualifications for all four Grand Slam events.  Partnering with Vanessa Henke, Alves took part in the 2005 Australian Open doubles event, but they lost to Daniela Hantuchová and Martina Navratilova in the first round. Bob Ryland (born 1920) is an American former tennis player and coach who is known for being the first African-American to play professional tennis.  Ryland has coached some of the world’s top-ranked professionals, including; Harold Solomon, Renee Blount, Leslie Allen, Arthur Ashe, Bruce Foxworth, Venus Williams and Serena Williams.  Ryland has also taught and coached at clubs in Bermuda, Puerto Rico, St. Alban’s Tennis Club in Washington, D.C. and the Mid-Town Tennis Club in Manhattan.  Ryland was inducted into the Wayne State University Athletic Hall of Fame (1991), Black Tennis Hall of Fame (2009), and the Eastern Tennis Hall of Fame in 2002, where he also received a Lifetime Achievement Award in 2012. Haroon Rahim, (born 12 November 1949) is a Pakistani former tennis player.  The former Pakistan and Asian No. 1, Rahim was the youngest tennis player ever to play for Pakistan in the Davis Cup at 15 years of age.  He was also the highest ranking Pakistani tennis player ever (a career-high singles ranking of World No. 44 in July 1977).  He led the UCLA team to victory with Jeff Borowiak and Jimmy Connors in 1970–71 and was 1971 NCAA doubles champion with Jeff Borowiak. Alex O'Brien (born March 7, 1970 in Amarillo, Texas) is a retired professional tennis player from the United States, who competed on the ATP Tour.  He became the world No. 1 doubles player in May 2000 and was ranked as high as world No. 30 in singles in June 1997. Fabiola Zuluaga (born 7 January 1979) is a retired professional tennis player from Colombia.  She retired on 9 September 2005.  She reached the Australian Open Semifinals in 2004 and became the first Colombian tennis player to reach a Grand Slam semifinal.  Fabiola is one of the best tennis players that Colombia has had (See Iván Molina).  She now lives in Bogotá. Stefanie Maria "Steffi" Graf (] ; born 14 June 1969) is a German former tennis player, who was ranked world No. 1 during her career.  Graf won 22 Grand Slam singles titles.  Her 22 singles titles put her second on the list of Major wins in the female competition since the introduction of the Open Era in 1968 and is third all-time behind Margaret Court (24) and Serena Williams (23).  In 1988, she became the first and only tennis player (male or female) to achieve the Golden Slam by winning all four Grand Slam singles titles and the Olympic gold medal in the same calendar year.  Furthermore, she is the only tennis player to have won each Grand Slam event at least four times. Iván Molina (born 16 June 1946) is a former professional Colombian tennis player. Anastasiya Andreyevna Myskina (Russian: Анастасия Андреевна Мыскина ; ] ; born 8 July 1981) is a Russian former tennis player.  She won the 2004 French Open singles title, becoming the first Russian female tennis player to win a Grand Slam singles title.  Subsequent to this victory, she rose to No. 3 in the WTA rankings, becoming the first Russian female tennis player to reach the top 3 in the history of the rankings.  In September 2004, she reached a career-high ranking of No. 2.  She has not officially retired, but has been inactive on the WTA Tour since May 2007.
Answer: Alex O'Brien