Question: when did the us first send troops to afghanistan
[{'answer': '7 October 2001', 'provenance': [{'wikipedia_id': '19666611', 'title': 'War in Afghanistan (2001–present)', 'start_paragraph_id': 1, 'start_character': 231, 'end_paragraph_id': 1, 'end_character': 245, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]