Question: when did senate rules change to 60 votes
[{'answer': '1975', 'provenance': [{'wikipedia_id': '26376415', 'title': 'Filibuster in the United States Senate', 'start_paragraph_id': 25, 'start_character': 3, 'end_paragraph_id': 25, 'end_character': 7, 'bleu_score': 1.0, 'section': 'Section::::History.:The two-track system, 60-vote rule and rise of the routine filibuster (1970 onward).\n'}]}, {'provenance': [{'wikipedia_id': '26376415', 'title': 'Filibuster in the United States Senate', 'start_paragraph_id': 25, 'start_character': 0, 'end_paragraph_id': 25, 'end_character': 637, 'bleu_score': 0.9813933169956551, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 2895734939693180581}, 'section': 'Section::::History.:The two-track system, 60-vote rule and rise of the routine filibuster (1970 onward).\n'}]}]