Question: when did the 1 child policy start in china
[{'answer': '1979', 'provenance': [{'wikipedia_id': '44664', 'title': 'One-child policy', 'start_paragraph_id': 1, 'start_character': 418, 'end_paragraph_id': 1, 'end_character': 422, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]