Question: In September 1939, when the Second World War begun, the then General Alfred Keller commanded the 4th Air Corps during the invasion of which countrty, he commanded Luftflotte 2, with his superior General Albert Kesselring, was a German "Luftwaffe Generalfeldmarschall" during World War II?
{'answer': 'Poland', 'supporting_facts': [['Alfred Keller', 0], ['Albert Kesselring', 0]]}