Question: what is the last book in the game of thrones
[{'answer': 'A Dream of Spring', 'provenance': [{'wikipedia_id': '12301', 'title': 'A Song of Ice and Fire', 'start_paragraph_id': 28, 'start_character': 331, 'end_paragraph_id': 28, 'end_character': 348, 'bleu_score': 1.0, 'section': 'Section::::Publishing history.:Planned novels and future.\n'}]}]