Question: when did puerto rico become part of the usa
[{'answer': 'Treaty of Paris', 'provenance': [{'wikipedia_id': '23041', 'title': 'Puerto Rico', 'start_paragraph_id': 3, 'start_character': 1217, 'end_paragraph_id': 3, 'end_character': 1232, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]