Question: who led the challenger expedition from 1872 to 1876
[{'answer': 'Captain George Nares', 'provenance': [{'wikipedia_id': '88284', 'title': 'Challenger expedition', 'start_paragraph_id': 2, 'start_character': 328, 'end_paragraph_id': 2, 'end_character': 348, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]