Question: when were assault rifles banned in the us
[{'answer': 'September 13 , 1994', 'provenance': [{'wikipedia_id': '40129756', 'title': 'Federal Assault Weapons Ban', 'start_paragraph_id': 2, 'start_character': 49, 'end_paragraph_id': 2, 'end_character': 68, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '40129756', 'title': 'Federal Assault Weapons Ban', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 343, 'bleu_score': 0.6602951420206921, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 12337313878651887903}, 'section': 'Section::::Abstract.'}]}]