Question: what kind of tube is used to produce x rays
[{'answer': 'X-ray tube', 'provenance': [{'wikipedia_id': '907899', 'title': 'X-ray tube', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 10, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '907899', 'title': 'X-ray tube', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 505, 'bleu_score': 0.573236349341372, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 18030719762412478845}, 'section': 'Section::::Abstract.'}]}]