Question: who has the highest rebound average in nba history
[{'answer': 'Wilt Chamberlain', 'provenance': [{'wikipedia_id': '26317175', 'title': 'List of National Basketball Association annual rebounding leaders', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 16, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]