Question: what is caleb's last name in pretty little liars
[{'answer': 'Rivers', 'provenance': [{'wikipedia_id': '27998609', 'title': 'List of Pretty Little Liars characters', 'start_paragraph_id': 72, 'start_character': 18, 'end_paragraph_id': 72, 'end_character': 24, 'bleu_score': 1.0, 'section': 'Section::::Acquaintances of Hanna Marin.:Relationships.\n'}]}]