Question: when did puerto rico become a territory of united states
[{'answer': '1898', 'provenance': [{'wikipedia_id': '23041', 'title': 'Puerto Rico', 'start_paragraph_id': 3, 'start_character': 1113, 'end_paragraph_id': 3, 'end_character': 1117, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]