Question: when did robbie douglas leave my three sons
[{'answer': '1971', 'provenance': [{'wikipedia_id': '174002', 'title': 'My Three Sons', 'start_paragraph_id': 9, 'start_character': 675, 'end_paragraph_id': 9, 'end_character': 679, 'bleu_score': 1.0, 'section': 'Section::::History.:Directors.\n'}]}]