Question: how many books are in the maus series
[{'answer': 'two volumes', 'provenance': [{'wikipedia_id': '349114', 'title': 'Maus', 'start_paragraph_id': 27, 'start_character': 138, 'end_paragraph_id': 27, 'end_character': 149, 'bleu_score': 1.0, 'section': 'Section::::Publication history.\n'}]}, {'provenance': [{'wikipedia_id': '349114', 'title': 'Maus', 'start_paragraph_id': 27, 'start_character': 0, 'end_paragraph_id': 27, 'end_character': 955, 'bleu_score': 0.9863473221773311, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17731564188442837114}, 'section': 'Section::::Publication history.\n'}]}]