Question: where did the first mass printing of books occur
[{'answer': 'Mainz , Germany', 'provenance': [{'wikipedia_id': '23295', 'title': 'Printing press', 'start_paragraph_id': 28, 'start_character': 165, 'end_paragraph_id': 28, 'end_character': 180, 'bleu_score': 1.0, 'section': 'Section::::The Printing Revolution.:Mass production and spread of printed books.\n'}]}, {'provenance': [{'wikipedia_id': '23295', 'title': 'Printing press', 'start_paragraph_id': 28, 'start_character': 0, 'end_paragraph_id': 28, 'end_character': 563, 'bleu_score': 0.979054689945215, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 10929767138942327740}, 'section': 'Section::::The Printing Revolution.:Mass production and spread of printed books.\n'}]}]