Question: when did the dh rule start in baseball
[{'answer': '1973', 'provenance': [{'wikipedia_id': '347297', 'title': 'Designated hitter', 'start_paragraph_id': 1, 'start_character': 130, 'end_paragraph_id': 1, 'end_character': 134, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '347297', 'title': 'Designated hitter', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 503, 'bleu_score': 0.946458428441119, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7855654303384534850}, 'section': 'Section::::Abstract.'}]}]