This combination of April 15, 2013 and April 2, 2014 photos show a police officer clearing Boylston Street following a bomb blast near the finish line of the 2013 Boston Marathon, and pedestrians crossing at the same corner nearly a year later in Boston. (Photo by Charles Krupa/AP Photo)

Tech. Sgt. Milo Hinson, 3rd Combat Camera Squadron, uses a flashlight while shooting a Berretta 9mm during the night-fire portion of Advance Weapons, Tactics and Techniques training in San Antonio. During night-fire training, airmen learn how to tactically illuminate targets with flashlights and practice using night vision goggles. (Photo by Staff Sgt. Jonathan Snyder/U.S. Air Force). 2011

David Goffin of Belgium meets a koala during a promotional event for the Australian Open tennis tournament at Melbourne Park on January 17, 2018. (Photo by Fiona Hamilton/Reuters/Tennis Australia)

Deacons attend a praying session during the Meskel Festival to commemorate the discovery of the true cross on which Jesus Christ was crucified on, at the Meskel Square in Ethiopia's capital Addis Ababa, September 26, 2016. (Photo by Tiksa Negeri/Reuters)

Women playing in the street as the snow falls on Johannesburg for the first time in seventeen years. (Photo by Keystone/Getty Images). 1st September 1962

Local residents crowd a swimming pool during a hot weather in Suining, Sichuan province, 27 July 2008. (Photo by Reuters/Stringer)

College students take shelter at a traffic point as a man paddles his rickshaw through a flooded road during heavy rain in Guwahati, India, June 13, 2017. (Photo by Anuwar Hazarika/Reuters)

A man carries a dog and wades through a flooded street in Chennai, in the southern Indian state of Tamil Nadu, Wednesday, December 2, 2015. Weeks of torrential rains have forced the airport in the state capital Chennai to close and have cut off several roads and highways, leaving tens of thousands of people stranded in their homes, government officials said Wednesday. (Photo by AP Photo)