Question: which group of artist is well known for painting en plein air
[{'answer': 'Barbizon school', 'provenance': [{'wikipedia_id': '24621', 'title': 'En plein air', 'start_paragraph_id': 3, 'start_character': 127, 'end_paragraph_id': 3, 'end_character': 142, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'answer': 'Hudson River School', 'provenance': [{'wikipedia_id': '24621', 'title': 'En plein air', 'start_paragraph_id': 3, 'start_character': 144, 'end_paragraph_id': 3, 'end_character': 163, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'answer': 'Impressionists', 'provenance': [{'wikipedia_id': '24621', 'title': 'En plein air', 'start_paragraph_id': 3, 'start_character': 169, 'end_paragraph_id': 3, 'end_character': 183, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'answer': 'The Newlyn School', 'provenance': [{'wikipedia_id': '24621', 'title': 'En plein air', 'start_paragraph_id': 6, 'start_character': 0, 'end_paragraph_id': 6, 'end_character': 17, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'provenance': [{'wikipedia_id': '24621', 'title': 'En plein air', 'start_paragraph_id': 6, 'start_character': 0, 'end_paragraph_id': 6, 'end_character': 349, 'bleu_score': 0.6605276833878381, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14603408411898525388}, 'section': 'Section::::History.\n'}]}]