Question: what does senior airman mean in the air force
[{'answer': 'fourth enlisted rank', 'provenance': [{'wikipedia_id': '561809', 'title': 'Senior airman', 'start_paragraph_id': 1, 'start_character': 27, 'end_paragraph_id': 1, 'end_character': 47, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '561809', 'title': 'Senior airman', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 551, 'bleu_score': 0.9531501622378341, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 8481802856379215668}, 'section': 'Section::::Abstract.'}]}]