Question: when did japan start planning the attack on pearl harbor
[{'answer': 'early spring 1941', 'provenance': [{'wikipedia_id': '60098', 'title': 'Attack on Pearl Harbor', 'start_paragraph_id': 17, 'start_character': 533, 'end_paragraph_id': 17, 'end_character': 550, 'bleu_score': 1.0, 'section': 'Section::::Background to conflict.:Military planning.\n'}]}, {'provenance': [{'wikipedia_id': '60098', 'title': 'Attack on Pearl Harbor', 'start_paragraph_id': 17, 'start_character': 0, 'end_paragraph_id': 17, 'end_character': 794, 'bleu_score': 0.984188478234951, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 312037827805859294}, 'section': 'Section::::Background to conflict.:Military planning.\n'}]}]