Question: who ruled the soviet union with sole power in a regime of terror
[{'answer': 'Stalin', 'provenance': [{'wikipedia_id': '21618309', 'title': 'Rise of Joseph Stalin', 'start_paragraph_id': 0, 'start_character': 15, 'end_paragraph_id': 0, 'end_character': 21, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '21618309', 'title': 'Rise of Joseph Stalin', 'start_paragraph_id': 38, 'start_character': 270, 'end_paragraph_id': 38, 'end_character': 1616, 'bleu_score': 0.9358948468577971, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 519088675410221856}, 'section': 'Section::::The Great Terror.\n'}]}]