Question: in north america power is generated at a frequency of
[{'answer': '60 Hz', 'provenance': [{'wikipedia_id': '488815', 'title': 'Utility frequency', 'start_paragraph_id': 1, 'start_character': 353, 'end_paragraph_id': 1, 'end_character': 358, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '488815', 'title': 'Utility frequency', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 447, 'bleu_score': 0.97451705556073, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 5394856144448947756}, 'section': 'Section::::Abstract.'}]}]