Based on the context and the answer, generate a question. 

Context: The TV was on ... but for some reason no one was paying attention . I think it was still really early ... like just the first plane had hit and everyone thought it was an accident still . So when the teacher came in she turned the TV off and said , ' If it 's important we 'll hear about it later . '

Answer:

11-Sep



What historical event is being described ?