Question: who said electrons occupy specific energy levels or shells
[{'answer': 'Niels Bohr', 'provenance': [{'wikipedia_id': '59444', 'title': 'Energy level', 'start_paragraph_id': 9, 'start_character': 245, 'end_paragraph_id': 9, 'end_character': 255, 'bleu_score': 1.0, 'section': 'Section::::History.\n'}]}, {'provenance': [{'wikipedia_id': '59444', 'title': 'Energy level', 'start_paragraph_id': 9, 'start_character': 0, 'end_paragraph_id': 9, 'end_character': 470, 'bleu_score': 0.9748377259086851, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1936927827320942928}, 'section': 'Section::::History.\n'}]}]