Question: what were the years of us involvement in the vietnam war
[{'answer': '1955 to 1975'}, {'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': 1432, 'bleu_score': 0.9692658767930771, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 17975787226949074482}, 'section': 'Section::::Abstract.'}]}]