Question: when did they start putting serial numbers on guns
[{'answer': '1968', 'provenance': [{'wikipedia_id': '320600', 'title': 'Gun Control Act of 1968', 'start_paragraph_id': 0, 'start_character': 19, 'end_paragraph_id': 0, 'end_character': 23, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '320600', 'title': 'Gun Control Act of 1968', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 303, 'bleu_score': 0.955027111100031, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16755514973898250471}, 'section': 'Section::::Abstract.'}]}]