Question: How many Grand Slam titles were won by the defending champion of the 1981 US Open - Women's Doubles?  

<P0-S0> The Williams sisters are two professional American tennis players: Venus Williams (b. 1980), a seven-time Grand Slam title winner (singles), and Serena Williams (b. 1981), twenty-three-time Grand Slam title winner (singles), both of whom were coached from an early age by their parents Richard Williams and Oracene Price. <P0-S1>  There is a noted professional rivalry between them – between the 2001 US Open and the 2017 Australian Open tournaments, they met in nine Grand Slam singles finals. <P0-S2>  They became the first two players, female or male, to play in 4 consecutive grand slam singles finals from the 2002 French Open to the 2003 Australian Open; Serena famously won all 4 to complete the first of two "Serena Slams". <P0-S3>  Between 2000 and 2016, a 17-year span, they collectively won 12 Wimbledon singles titles (Venus won 5 and Serena won 7). <P0-S4>  By winning the 2001 Australian Open women's doubles title, they became the 5th pair to complete the Career Doubles Grand Slam and the only pair to complete the Career Doubles Golden Slam. <P0-S5>  At the time, Venus and Serena were only 20 and 19 years old, respectively. <P0-S6>  Since then they have gone on to add another two Olympic gold medals in the 2008 Beijing Olympics and the 2012 London Olympics. <P0-S7>  Nearly a decade later, the duo would go on to win 4 consecutive grand slam doubles titles from 2009 Wimbledon through 2010 Roland Garros, which would catapult them to co-No. <P0-S8>  1 doubles players on 7 June 2010. <P0-S9>  Two weeks later, on 21 June 2010, Serena would hold the No. 1 singles ranking and Venus would be right behind her at No. 2 in singles. <P0-S10>  Their most recent grand slam doubles titles came at the 2012 Wimbledon & 2016 Wimbledon events. <P0-S11>  They remain very close, often watching each other's matches in support, even after one of them has been knocked out of a tournament. <SEP> <P1-S0> Pam Teeguarden (born April 17, 1951) is a former American professional tennis player in the 1970s and 1980s, ranked in the top 20 from 1970–1975, according to "John Dolan's Women's Tennis Ultimate Guide", prior to computer rankings. <P1-S1>  She won two Grand Slam Doubles Titles and was a quarter finalist in singles at the U.S. Open and The French Open. <P1-S2>  Her father Jerry, a well known coach, helped Margaret Court win the coveted Grand Slam (all four Grand Slam titles in one year) in 1970 and Virginia Wade to her 1977 Wimbledon triumph. <P1-S3>  Teeguarden was voted the "Most Watchable Player" based on play and appearance by a group of Madison Avenue advertising executives or "Mad Men" while playing at the US Open. <P1-S4>  Teeguarden played in 19 consecutive US Opens, holding the record until Chris Evert played in 20. <P1-S5>  She wore the first all black outfit in the history of tennis in 1975 at The Bridgestone Doubles Championships in Tokyo, starting a trend that is still popular today. <P1-S6>  Teeguarden was the first woman tennis player signed by Nike. <P1-S7>  She played on the victorious Los Angeles Strings Team Tennis team in 1981 and won the Team Tennis Mixed Doubles Division with Tom Gullikson in 1977; they were also runners-up in the league that year. <SEP> <P2-S0> Billie Jean King ("née" Moffitt; born November 22, 1943) is an American former World No. 1 professional tennis player. <P2-S1>  King won 39 Grand Slam titles: 12 in singles, 16 in women's doubles, and 11 in mixed doubles. <P2-S2>  King won the singles title at the inaugural WTA Tour Championships. <P2-S3>  King often represented the United States in the Federation Cup and the Wightman Cup. <P2-S4>  She was a member of the victorious United States team in seven Federation Cups and nine Wightman Cups. <P2-S5>  For three years, King was the United States' captain in the Federation Cup. <SEP> <P3-S0> Billie Jean King and Martina Navratilova were the defending champions but only Navratilova competed that year with Pam Shriver.