Former Olympic and world 100 metres champion Maurice Greene of the US answers a question during an interview at Beijing Sport University February 4, 2008. Greene announced his retirement from athletics on Monday. "Today I'm officially announcing my retirement from the sport," the 33-year-old American told reporters in Beijing. Greene won Olympic 100 metres gold at the 2000 Sydney Games and was the first man to win the 100m and 200m titles at a single world championships in Seville in 1999. [Agencies]