Question: when did seat belts become mandatory in the us
[{'answer': 'January 1 , 1968', 'provenance': [{'wikipedia_id': '11749520', 'title': 'Seat belt laws in the United States', 'start_paragraph_id': 1, 'start_character': 234, 'end_paragraph_id': 1, 'end_character': 250, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '11749520', 'title': 'Seat belt laws in the United States', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 782, 'bleu_score': 0.8394678342734351, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15352952824599766894}, 'section': 'Section::::Abstract.'}]}]