Question: What professional sport did Sun Tiantian and Lucie Hradecká both play?

Context paragraphs:
2014 US Open – Women's Doubles: Andrea Hlaváčková and Lucie Hradecká were the defending champions, but chose not to participate together.  Hlaváčková played alongside Zheng Jie, but lost in the quarterfinals to Kimiko Date-Krumm and Barbora Záhlavová-Strýcová.  Hradecká teamed up with Michaëlla Krajicek, but lost in the third round to Zarina Diyas and Xu Yifan. <br>

2011 International Country Cuneo – Doubles: Eva Birnerová and Lucie Hradecká were the defending champions, but Hradecká chose not to participate.

2008 Banka Koper Slovenia Open – Doubles: Lucie Hradecká and Renata Voráčová were the defending champions, but Voráčová chose not to participate, and only Hradecká competed that year.  Hradecká partnered up with Andreja Klepač, but they lost in the quarterfinals to Vera Dushevina and Ekaterina Makarova.

2015 J&amp;T Banka Prague Open – Doubles: Lucie Hradecká and Michaëlla Krajicek were the defending champions, but Hradecká chose not to participate this year.  Krajicek played alongside Karolína Plíšková, but lost in the quarterfinals to Belinda Bencic and Kateřina Siniaková.

2017 Coupe Banque Nationale – Doubles: Andrea Hlaváčková and Lucie Hradecká were the defending champions, but decided not to compete together.  Hradecká partnered with Barbora Krejčíková, but lost in the quarterfinals to Bianca Andreescu and Carson Branstine.  Hlaváčková partnered with Tímea Babos and successfully defended her title, defeating Andreescu and Branstine 6–3, 6–1 in the final.

Lucie Hradecká: Lucie Hradecká (] ; born 21 May 1985 in Prague) is a professional tennis player from the Czech Republic.  In her career, Hradecká has won 19 WTA doubles titles, and two Grand Slam titles, the 2011 French Open and the 2013 US Open, partnered both times by fellow Czech Andrea Hlaváčková.  The pair are also the 2012 Olympic silver medallists in doubles.  She has also won a mixed doubles Grand Slam title, the 2013 French Open with František Čermák.  Her biggest singles career highlight to date was defeating former world number one Ana Ivanovic in the first round of the 2015 Australian Open.

2012 Gastein Ladies – Doubles: Eva Birnerová and Lucie Hradecká were the defending champions but Hradecká decided not to participate. <br>

Sun Tiantian: Sun Tiantian (; ; born 12 October 1981) is a Chinese former professional tennis player.

2014 French Open – Mixed Doubles: Lucie Hradecká and František Čermák were the defending champions, but Čermák chose not to participate this year.  Hradecká played alongside Mariusz Fyrstenberg but lost in the second round to the eventual champions Anna-Lena Grönefeld and Jean-Julien Rojer.

2011 Dow Corning Tennis Classic – Doubles: Laura Granville and Lucie Hradecká were the defending champions, however Granville did not participate.  Lucie Hradecká partnered up with Marina Erakovic and lost in the first round to Beatrice Capra and Coco Vandeweghe

Supporting paragraphs: Sun Tiantian Lucie Hradecká
Answer: professional tennis