Two Argentine pairs were crowned winners of the world tango championships in Buenos Aires, the city government said Saturday. More than 20,000 people attended the music and dance shows during the competition, organizers said, with a final showdown on a stage in front of the historic Buenos Aires Obelisk in the heart of Argentina’s capital. In the stage category, which featured spectacular acrobatic stunts, Constanza Vieyto and Ricardo Astrada from the city of Pergamino beat 19 other couples to emerge champions. Forty pairs vied for the title in the traditional or “salon” category, dancing a tango that originated in Buenos Aires, with the crown going to Cynthia Palacios and Sebastian Bolivar from the city of Cipolletti. The world championships, held from September 6 to 18, involved 560 couples from 30 countries, including the United States, France, Russia, Japan and the Philippines.