Question: when did little league start using aluminum bats
[{'answer': '1971', 'provenance': [{'wikipedia_id': '432366', 'title': 'Little League Baseball', 'start_paragraph_id': 31, 'start_character': 0, 'end_paragraph_id': 31, 'end_character': 4, 'bleu_score': 1.0, 'section': 'Section::::History.:Timeline.:International era.\n'}]}, {'provenance': [{'wikipedia_id': '432366', 'title': 'Little League Baseball', 'start_paragraph_id': 31, 'start_character': 0, 'end_paragraph_id': 31, 'end_character': 344, 'bleu_score': 0.9657992495762461, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14589699484152538827}, 'section': 'Section::::History.:Timeline.:International era.\n'}]}]