Question: when did sound become a regular part of the motion picture viewing experience
[{'answer': '1929', 'provenance': [{'wikipedia_id': '10783', 'title': 'History of film', 'start_paragraph_id': 120, 'start_character': 47, 'end_paragraph_id': 120, 'end_character': 51, 'bleu_score': 1.0, 'section': 'Section::::Sound era.\n'}]}]