Task: Question Generation
Input (English): Context : The Gleiwitz incident (German: Überfall auf den Sender Gleiwitz; Polish: Prowokacja gliwicka) was a false flag operation by Nazi forces posing as Poles on 31 August 1939, against the German radio station Sender Gleiwitz in Gleiwitz, Upper Silesia, Germany (since 1945: Gliwice, Poland) on the eve of World War II in Europe. 
Subject : Gleiwitz incident 
Relation : point in time
Output (English): On what date did Gleiwitz incident occur?