By Eric Kelsey LOS ANGELES (Reuters) – Sports Illustrated magazine on Thursday unveiled its annual swimsuit issue with models Nina Agdal, Lily Aldridge and Chrissy Teigen on the cover of its 50th anniversary edition. Agdal, 21, from Denmark, and Americans Teigen and Aldridge, both 28, are the latest models to win a spot on the cover of the magazine’s swimsuit issue, which has boasted the likes of Heidi Klum, Elle Macpherson, Tyra Banks and Kate Upton on its cover early in their careers.