Question: when was the last halley's comet seen
[{'answer': '1986', 'provenance': [{'wikipedia_id': '46083', 'title': "Halley's Comet", 'start_paragraph_id': 1, 'start_character': 190, 'end_paragraph_id': 1, 'end_character': 194, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]