Question: venus's atmosphere has much more carbon dioxide than earth's because
[{'answer': 'A runaway greenhouse effect', 'provenance': [{'wikipedia_id': '6410946', 'title': 'Atmosphere of Venus', 'start_paragraph_id': 3, 'start_character': 536, 'end_paragraph_id': 3, 'end_character': 563, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '6410946', 'title': 'Atmosphere of Venus', 'start_paragraph_id': 3, 'start_character': 0, 'end_paragraph_id': 3, 'end_character': 684, 'bleu_score': 0.981898582188057, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 5825192669658561850}, 'section': 'Section::::Abstract.'}]}]