Question: when did radio become popular in the us
[{'answer': 'in the 1920s', 'provenance': [{'wikipedia_id': '1598357', 'title': 'Radio in the United States', 'start_paragraph_id': 5, 'start_character': 66, 'end_paragraph_id': 5, 'end_character': 78, 'bleu_score': 1.0, 'section': 'Section::::Overview.\n'}]}]