Protesters on a rooftop use a slingshot to throw stones at riot police during clashes outside Hong Kong Polytechnic University (PolyU) in Hong Kong, China November 17, 2019. Hundreds of defiant protesters inside Hong Kong's Polytechnic University started fires at the school's entrance to prevent police from entering, while police water cannon and armoured vehicles were deployed in raging battles that lasted an entire day and into the night. REUTERS/Thomas Peter