Question: when did catalytic converters become mandatory in us
[{'answer': '1975', 'provenance': [{'wikipedia_id': '286802', 'title': 'Catalytic converter', 'start_paragraph_id': 2, 'start_character': 251, 'end_paragraph_id': 2, 'end_character': 255, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '286802', 'title': 'Catalytic converter', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 758, 'bleu_score': 0.9209753637102511, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 9269687576039267486}, 'section': 'Section::::Abstract.'}]}]