Question: when did puerto rico become a u.s. territory
[{'answer': 'April 11 , 1899', 'provenance': [{'wikipedia_id': '23041', 'title': 'Puerto Rico', 'start_paragraph_id': 43, 'start_character': 292, 'end_paragraph_id': 43, 'end_character': 307, 'bleu_score': 1.0, 'section': 'Section::::History.:American colony (1898–present).\n'}]}]