Opposition students march against Venezuelan President Nicolas Maduro's government in Caracas February 12, 2015. Venezuelan troops blocked students during marches against Maduro on Thursday as pro-government supporters also rallied on the anniversary of 2014 protests that led to 43 deaths. In Caracas, troops cordoned off scores of students on an unauthorized march to a church where they planned a mass in honour of demonstrators who died. (Photo by Jorge Silva/Reuters)

A dog is kept at a pen at the newly opened Central Zoo in Pyongyang, North Korea, Tuesday, August 23, 2016. One of the most popular attractions at the zoo might come as a surprise to foreign visitors. Just across the way from the hippopotamus pen and the reptile house, dozens of varieties of dogs, including schnauzers, German shepherds, Shih Tzus and Saint Bernards – are on display in the “dog pavilion”. (Photo by Dita Alangkara/AP Photo)

A newly married bride is seen after a mass wedding ceremony in which 2,016 couples participated, at Zocalo square in Mexico City, Mexico, March 19, 2016. Thousands of couples took part in a mass wedding ceremony Saturday in Mexico City. More than 5,000 people descended on Mexico City’s central square for the festivities. Among them were 2,165 couples ready to get married. (Photo by Edgard Garrido/Reuters)

Ugly dog contestants Sweepee Rambo and owner Jason Wurtz celebrate in winning the 2016 World's Ugliest Dog Contest at the Sonoma-Marin Fair in Petaluma, California, USA, 24 June 2016. (Photo by Peter Dasilva/EPA)

A man carries an injured girl after what activists said were five air strikes by forces loyal to Syria's President Bashar al-Assad in Douma, eastern al-Ghouta, near Damascus September 11, 2014. (Photo by Bassam Khabieh/Reuters)

Workers clean empty cooking oil containers at a roadside recycling workshop in Kolkata, India, July 13, 2016. (Photo by Rupak De Chowdhuri/Reuters)

Cambodian children sleep on a pavement at a park in Phnom Penh on July 8, 2016. (Photo by Tang Chhin Sothy/AFP Photo)

A tourist poses on the glass-bottom bridge at Zhangjiajie Grand Canyon on August 20, 2016 in Zhangjiajie, Hunan Province of China. The Zhangjiajie Grand Canyon's glass-bottomed bridge welcame its trial operation on Saturday and about 8,000 tourists crowded to view the grand glass bridge. (Photo by VCG/VCG via Getty Images)