Question: when did the royal flying corps became the raf
[{'answer': '1918', 'provenance': [{'wikipedia_id': '233670', 'title': 'Royal Flying Corps', 'start_paragraph_id': 1, 'start_character': 164, 'end_paragraph_id': 1, 'end_character': 168, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]