Question: when did 18 year olds get the right to vote in the us
[{'answer': '1971', 'provenance': [{'wikipedia_id': '70136', 'title': 'Twenty-sixth Amendment to the United States Constitution', 'start_paragraph_id': 1, 'start_character': 294, 'end_paragraph_id': 1, 'end_character': 298, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]