Question: what are the balls that grow on oak trees
[{'answer': 'Oak apple or oak gall', 'provenance': [{'wikipedia_id': '5326576', 'title': 'Oak apple', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 21, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '5326576', 'title': 'Oak apple', 'start_paragraph_id': 1, 'start_character': 4, 'end_paragraph_id': 1, 'end_character': 922, 'bleu_score': 0.8485909082813451, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 8353317683879628237}, 'section': 'Section::::Abstract.'}]}]