Two police officers patrol at St. Pancras Station in London, Thursday, July 26, 2012. Opening ceremonies for the 2012 London Olympics will be held Friday, July 27. (AP Photo/Emilio Morenatti)

A slalom canoeist empties his canoe during a training session at the Lee Valley Whitewater Center, ahead of the 2012 Summer Olympics, Thursday, July 26, 2012, in London. (AP Photo/Kirsty Wigglesworth)

An athlete practices her stance off to the side of the training area for the 10-meter pistol, at the Royal Artillery Barracks ahead of the start of the 2012 Summer Olympics, Thursday, July 26, 2012, in London. (AP Photo/Rebecca Blackwell)

South Korean riders train for the 2012 Summer Olympics, Thursday, July 26, 2012, in London. (AP Photo/Christophe Ena)

U.S. gymnast Mc Kayla Maroney performs on the vault during training at the 2012 Summer Olympics, Thursday, July 26, 2012, in London. (AP Photo/Julie Jacobson)

U.S. gymnast Kyla Ross performs on the beam during training at the 2012 Summer Olympics, Thursday, July 26, 2012, in London. (AP Photo/Gregory Bull)

Italy's Vanessa Ferrari strikes a pose as she performs on the beam during training at the 2012 Summer Olympics, Thursday, July 26, 2012, in London. (AP Photo/Julie Jacobson)

An Australian gymnast performs on the uneven bars during training at the 2012 Summer Olympics, Thursday, July 26, 2012, in London. (AP Photo/Gregory Bull)

United Arab Emirates' Ismaeil Matar, obscured, bottom left, is congratulated by jubilant teammates after scoring agains Uruguay during their group A men's soccer match at the London 2012 Summer Olympics, Thursday, July 26, 2012 at Old Trafford Stadium in Manchester, England. (AP Photo/Jon Super)

An Australian gymnast performs on the floor during training at the 2012 Summer Olympics, Thursday, July 26, 2012, in London. (AP Photo/Matt Dunham)

A diver plunges in the pool during a practice session at the Aquatics Center at the Olympic Park ahead of the 2012 Summer Olympics, Thursday, July 26, 2012, in London. Opening ceremonies for the 2012 London Olympics will be held Friday, July 27. (AP Photo/Daniel Ochoa De Olza)

Single sculls, in foreground, train on Dorney l Lake in Eton Dorney, near Windsor, England, at the 2012 Summer Olympics, Thursday, July 26, 2012. The Olympic rowing competition starts on Saturday. (AP Photo/Natacha Pisarenko)

In this multiple exposure photo, a Brazilian gymnast performs on the vault during training at the 2012 Summer Olympics, Thursday, July 26, 2012, in London. (AP Photo/Julie Jacobson)

In this multiple exposure photo, a Brazilian gymnast runs to perform on the vault during training at the 2012 Summer Olympics, Thursday, July 26, 2012, in London. (AP Photo/Julie Jacobson)

A swimmer floats in the pool during a practice at the Aquatics Center at the Olympic Park ahead of the 2012 Summer Olympics, Thursday, July 26, 2012, in London. Opening ceremonies for the 2012 London Olympics will be held Friday, July 27. (AP Photo/Mark J. Terrill)

Swimmers practice at the Aquatics Center at the Olympic Park ahead of the 2012 Summer Olympics, Thursday, July 26, 2012, in London. Opening ceremonies for the 2012 London Olympics will be held Friday, July 27. (AP Photo/Mark J. Terrill)