 Complete the following phrase:  Mixed doubles is played the same as doubles, but with one man and one woman per team. This form of tennis is rare in the professional game because the mens and womens tours are organised separately by the ATP and WTA, respectively. However, all four Grand Slam tournaments hold a mixed doubles competition, alongside the mens and womens doubles, featuring many of the same players. There is also an annual mixed tournament for national teams, the Hopman Cup, which includes mixed doubles matches. Additionally, there have been mixed doubles events at the Summer Olympics on various occasions In 1900, from 1912 until 1920 and again since 