Question: when did the open era begin in tennis
[{'answer': '1968', 'provenance': [{'wikipedia_id': '221421', 'title': 'Rod Laver', 'start_paragraph_id': 1, 'start_character': 242, 'end_paragraph_id': 1, 'end_character': 246, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '221421', 'title': 'Rod Laver', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 287, 'bleu_score': 0.6464452859719381, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17895485939806184439}, 'section': 'Section::::Abstract.'}]}]