Question: why is mtbe used as a gasoline additive
[{'answer': 'to prevent engine knocking', 'provenance': [{'wikipedia_id': '391568', 'title': 'Methyl tert-butyl ether', 'start_paragraph_id': 7, 'start_character': 132, 'end_paragraph_id': 7, 'end_character': 158, 'bleu_score': 1.0, 'section': 'Section::::Uses.:As anti-knocking agent.\n'}]}, {'provenance': [{'wikipedia_id': '391568', 'title': 'Methyl tert-butyl ether', 'start_paragraph_id': 7, 'start_character': 0, 'end_paragraph_id': 7, 'end_character': 449, 'bleu_score': 0.970362113628587, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 13689588488445694977}, 'section': 'Section::::Uses.:As anti-knocking agent.\n'}]}]