An actor plays an injured passer-by during Exercise Strong Tower, the scene of a mock terror attack at a disused underground station in central London, Britain June 30, 2015. London police held their biggest-ever terrorism drill on Tuesday, pitting the emergency services against a group of marauding attackers, nearly 10 years since four young British Islamists killed 52 people in suicide bombings on London's transport network in July 2005. (Photo by Peter Nicholls/Reuters)

A reveller takes part in an annual block party known as “Ceu na Terra” (Heaven on Earth), one of the many carnival parties to take place in the neighbourhoods of Rio de Janeiro, January 30, 2016. (Photo by Pilar Olivares/Reuters)

A wolf looks into the camera at the 30 km (19 miles) exclusion zone around the Chernobyl nuclear reactor in the abandoned village of Orevichi, Belarus, March 2, 2016. What happens to the environment when humans disappear? Thirty years after the Chernobyl nuclear disaster, booming populations of wolf, elk and other wildlife in the vast contaminated zone in Belarus and Ukraine provide a clue. (Photo by Vasily Fedosenko/Reuters)

A man waits for Queen Beatrix's abdication ceremony outside the Royal Palace in Amsterdam April 30, 2013. The Netherlands is celebrating Queen's Day on Tuesday, which will also mark the abdication of Queen Beatrix and the investiture of her eldest son Willem-Alexander. (Photo by Paul Vreeker/Reuters)

Hindu women worship the Sun god Surya in the polluted waters of the river Yamuna during the Hindu religious festival of Chatt Puja in New Delhi October 30, 2014. Hindu women fast for the whole day for the betterment of their family and the society during the festival. (Photo by Ahmad Masood/Reuters)

Twenty five life-size donkeys have been given pride of place in St Paul's Cathedral as part of an interfaith exhibition. They've been painted by Egyptian and Western artists, to show solidarity for the people of Egypt. Photo: Artist painted donkey statues are displayed in the “Caravan” exhibition on August 30, 2013 in London, England. (Photo by Peter Macdiarmid)

A stunt rider jumps over spectators after the final stage of the annual ABSA Cape Epic mountain bike stage race, Cape Town, South Africa, 30 March 2014. The multi day stage race is know as the “Tour de France” of mountain biking and sees 1,200 riders riding 720km in seven days. The race includes the worlds leading professional racers along with amateur cyclists. (Photo by Kim Ludbrook/EPA)