Question: what type of surface is the us open played on
[{'answer': 'hard courts', 'provenance': [{'wikipedia_id': '30311', 'title': 'Tennis court', 'start_paragraph_id': 7, 'start_character': 235, 'end_paragraph_id': 7, 'end_character': 246, 'bleu_score': 1.0, 'section': 'Section::::Surfaces.\n'}]}, {'provenance': [{'wikipedia_id': '30311', 'title': 'Tennis court', 'start_paragraph_id': 13, 'start_character': 0, 'end_paragraph_id': 13, 'end_character': 628, 'bleu_score': 0.968732807714302, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4209676581789405515}, 'section': 'Section::::Surfaces.\n'}]}]