Question: when did the british army first go to afghanistan
[{'answer': '1839', 'provenance': [{'wikipedia_id': '510534', 'title': 'First Anglo-Afghan War', 'start_paragraph_id': 1, 'start_character': 172, 'end_paragraph_id': 1, 'end_character': 176, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]