Question: when did pitbulls become illegal in the uk
[{'answer': '1991', 'provenance': [{'wikipedia_id': '1007738', 'title': 'Dangerous Dogs Act 1991', 'start_paragraph_id': 0, 'start_character': 19, 'end_paragraph_id': 0, 'end_character': 23, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]