Question: when did tokyo become the capital of japan
[{'answer': '1941', 'provenance': [{'wikipedia_id': '494807', 'title': 'Capital of Japan', 'start_paragraph_id': 4, 'start_character': 3, 'end_paragraph_id': 4, 'end_character': 7, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}]