Question: when did american schools become gun free zones
[{'answer': '1990', 'provenance': [{'wikipedia_id': '3297764', 'title': 'Gun-Free School Zones Act of 1990', 'start_paragraph_id': 0, 'start_character': 29, 'end_paragraph_id': 0, 'end_character': 33, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '3297764', 'title': 'Gun-Free School Zones Act of 1990', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 221, 'bleu_score': 0.9092777304123971, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 9290516209200866425}, 'section': 'Section::::Abstract.'}]}]