The headquarters of the European Central Bank (ECB) are pictured in Frankfurt, Germany September 8, 2016. REUTERS/Ralph Orlowski/File Photo

British Prime Minister Theresa May enters the General Assembly Hall to speak during the 71st United Nations General Assembly in Manhattan, New York, U.S. September 20, 2016. REUTERS/Eduardo Munoz

A pair of African Elephants nuzzle up to each other at the Mokolodi Nature Reserve in Gaborone, Botswana July 10, 2003. REUTERS/Jason Reed/File Photo

Foreign tourists in safari riverboats observe elephants along the Chobe river bank near Botswana's northern border where Zimbabwe, Zambia and Namibia meet, March 4, 2005. REUTERS/Peter Apps/File Photo

Cranes are seen on the construction site of Frankfurt's university campus in Frankfurt, Germany, April 15, 2016. REUTERS/Kai Pfaffenbach

People walk through the Canary Wharf, the business and financial district in London, Britain, September 8, 2016. REUTERS/Kevin Coombs

A U.S. Air Force B-1B bomber lands Osan Air Base in Pyeongtaek, South Korea, September 21, 2016. Yonhap/via REUTERS

A U.S. Air Force B-1B bomber lands Osan Air Base in Pyeongtaek, South Korea, September 21, 2016. Yonhap/via REUTERS