Question: when did pluto lose its classification as a proper planet
[{'answer': '2006', 'provenance': [{'wikipedia_id': '44469', 'title': 'Pluto', 'start_paragraph_id': 2, 'start_character': 441, 'end_paragraph_id': 2, 'end_character': 445, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '44469', 'title': 'Pluto', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 551, 'bleu_score': 0.978375183951072, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 18379706608027521784}, 'section': 'Section::::Abstract.'}]}]