Question: what is the meaning of clean air act
[{'answer': 'control air pollution', 'provenance': [{'wikipedia_id': '19060778', 'title': 'Clean Air Act (United States)', 'start_paragraph_id': 1, 'start_character': 80, 'end_paragraph_id': 1, 'end_character': 101, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '19060778', 'title': 'Clean Air Act (United States)', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 533, 'bleu_score': 0.9030821421670621, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7696628008956147337}, 'section': 'Section::::Abstract.'}]}]