Question: when was the last b 52 bomber built
[{'answer': '1962', 'provenance': [{'wikipedia_id': '18933037', 'title': 'Boeing B-52 Stratofortress', 'start_paragraph_id': 20, 'start_character': 476, 'end_paragraph_id': 20, 'end_character': 480, 'bleu_score': 1.0, 'section': 'Section::::Development.:Pre-production and production.\n'}]}, {'provenance': [{'wikipedia_id': '18933037', 'title': 'Boeing B-52 Stratofortress', 'start_paragraph_id': 20, 'start_character': 0, 'end_paragraph_id': 20, 'end_character': 554, 'bleu_score': 0.7495751880693411, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 5474937404340458360}, 'section': 'Section::::Development.:Pre-production and production.\n'}]}]