Question: which big three allied leaders met at teheran in 1943
[{'answer': 'Joseph Stalin', 'provenance': [{'wikipedia_id': '70381', 'title': 'Tehran Conference', 'start_paragraph_id': 1, 'start_character': 67, 'end_paragraph_id': 1, 'end_character': 80, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'Franklin D. Roosevelt', 'provenance': [{'wikipedia_id': '70381', 'title': 'Tehran Conference', 'start_paragraph_id': 1, 'start_character': 82, 'end_paragraph_id': 1, 'end_character': 103, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'Winston Churchill', 'provenance': [{'wikipedia_id': '70381', 'title': 'Tehran Conference', 'start_paragraph_id': 1, 'start_character': 109, 'end_paragraph_id': 1, 'end_character': 126, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '70381', 'title': 'Tehran Conference', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 1002, 'bleu_score': 0.9502602021600861, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 2708512708670404712}, 'section': 'Section::::Abstract.'}]}]