Question: what does the x mean in x ray
[{'answer': 'unknown type of radiation', 'provenance': [{'wikipedia_id': '34197', 'title': 'X-ray', 'start_paragraph_id': 1, 'start_character': 568, 'end_paragraph_id': 1, 'end_character': 593, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '34197', 'title': 'X-ray', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 693, 'bleu_score': 0.57777096959644, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10440032878476121885}, 'section': 'Section::::Abstract.'}]}]