A boy holds a banner written with "Keep running daddy" to support his father, who is a participant of the 2013 London Marathon held in London, Britain on April 21, 2013. (Xinhua/Bimal Gautam)

A blade runner take part in the 2013 London Marathon held in London, Britain on April 21, 2013. (Xinhua/Bimal Gautam)

Securities work with explosive-detecting dogs at runway of the 2013 London Marathon held in London, Britain on April 21, 2013. (Xinhua/Bimal Gautam)

Runners take part in the London Marathon, in London, capital of Britain, on April 21, 2013. (Xinhua/Bimal Gautam)

Runners take part in the London Marathon, in London, capital of Britain, on April 21, 2013. (Xinhua/Bimal Gautam)