Question: what is the most important gas in the greenhouse effect
[{'answer': 'carbon dioxide', 'provenance': [{'wikipedia_id': '21350772', 'title': 'Greenhouse gas', 'start_paragraph_id': 1, 'start_character': 241, 'end_paragraph_id': 1, 'end_character': 255, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '21350772', 'title': 'Greenhouse gas', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 651, 'bleu_score': 0.6698889842615441, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 13936865830710859617}, 'section': 'Section::::Abstract.'}]}]