Question: name one man made source of background radiation
[{'answer': 'nuclear weapons testing', 'provenance': [{'wikipedia_id': '4882', 'title': 'Background radiation', 'start_paragraph_id': 2, 'start_character': 280, 'end_paragraph_id': 2, 'end_character': 303, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '4882', 'title': 'Background radiation', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 325, 'bleu_score': 0.518120571017418, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4447441273291011545}, 'section': 'Section::::Abstract.'}]}]