Question: how long was america's involvement in the vietnam war
[{'answer': '20 long years', 'provenance': [{'wikipedia_id': '8453309', 'title': 'Role of the United States in the Vietnam War', 'start_paragraph_id': 1, 'start_character': 202, 'end_paragraph_id': 1, 'end_character': 215, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '8453309', 'title': 'Role of the United States in the Vietnam War', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 1423, 'bleu_score': 0.8342572995323291, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 12967221859119316716}, 'section': 'Section::::Abstract.'}]}]