Question: when did the british expeditionary force go to france
[{'answer': 'September 1939', 'provenance': [{'wikipedia_id': '19942628', 'title': 'British Expeditionary Force (World War II)', 'start_paragraph_id': 1, 'start_character': 124, 'end_paragraph_id': 1, 'end_character': 138, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]