Question: when did tennis balls changed from white to yellow
[{'answer': '1972', 'provenance': [{'wikipedia_id': '1577192', 'title': 'Tennis ball', 'start_paragraph_id': 3, 'start_character': 407, 'end_paragraph_id': 3, 'end_character': 411, 'bleu_score': 1.0, 'section': 'Section::::Specifications.\n'}]}, {'provenance': [{'wikipedia_id': '1577192', 'title': 'Tennis ball', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 481, 'bleu_score': 0.802598343442913, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 13194327225309273564}, 'section': 'Section::::Specifications.\n'}]}]