Multi-Olympic medallist, former U.S. sprinter Michael Johnson joins children to run on a specially laid track inside the Olympic Stadium under construction, in the Olympic Park, east London, Britain, July 27, 2010. Tuesday marks exactly two years to go until the opening ceremony of the London 2012 Olympic Games. The London Organising Committee of the Olympic Games and Paralympic Games (LOCOG) and the London City Hall launched the Volunteering Programme and the flagship shop of London 2012 on the day. (Xinhua/LOCOG)

London Mayor Boris Johnson (C), chairman of the London Organising Committee of the Olympic Games and Paralympic Games (LOCOG) Sebastian Coe (L)and Britain's Sport and Olympics Minister Hugh Robertson (R) launch the flagship shop of London 2012 at the St. Pancras rail station in London, Britain, July 27, 2010. Tuesday marks exactly two years to go until the opening ceremony of the London 2012 Olympic Games. The London Organising Committee of the Olympic Games and Paralympic Games (LOCOG) and the London City Hall launched the Volunteering Programme and the flagship shop of London 2012 on the day. (Xinhua/LOCOG)

London Mayor Boris Johnson tries a test ride in the velodrome under construction, in the Olympic Park, east London, Britain, July 27, 2010. Tuesday marks exactly two years to go until the opening ceremony of the London 2012 Olympic Games. The London Organising Committee of the Olympic Games and Paralympic Games (LOCOG) and the London City Hall launched the Volunteering Programme and the flagship shop of London 2012 on the day. (Xinhua/LOCOG)

London Mayor Boris Johnson (2nd R, C) and chairman of the London Organising Committee of the Olympic Games and Paralympic Games (LOCOG) Sebastian Coe (3rd R, C) join volunteers to launch the London 2012 Volunteering Programme at the St. Pancras rail station in London, Britain, July 27, 2010. Tuesday marks exactly two years to go until the opening ceremony of the London 2012 Olympic Games. LOCOG and the London City Hall launched the Volunteering Programme and the flagship shop of London 2012 on the day. (Xinhua/LOCOG)