Question: when did us get involved in vietnam war
[{'answer': '1955', 'provenance': [{'wikipedia_id': '8453309', 'title': 'Role of the United States in the Vietnam War', 'start_paragraph_id': 1, 'start_character': 137, 'end_paragraph_id': 1, 'end_character': 141, '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': 144, 'bleu_score': 0.8945648481322711, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3236339397252386522}, 'section': 'Section::::Abstract.'}]}]