Question: when did the us officially enter the vietnam war
[{'answer': 'September 1950', 'provenance': [{'wikipedia_id': '8453309', 'title': 'Role of the United States in the Vietnam War', 'start_paragraph_id': 19, 'start_character': 12, 'end_paragraph_id': 19, 'end_character': 26, 'bleu_score': 1.0, 'section': 'Section::::Timeline.:Harry S. Truman (1945–53).\n'}]}, {'provenance': [{'wikipedia_id': '8453309', 'title': 'Role of the United States in the Vietnam War', 'start_paragraph_id': 19, 'start_character': 0, 'end_paragraph_id': 19, 'end_character': 330, 'bleu_score': 0.962600167205617, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 7253244142729265685}, 'section': 'Section::::Timeline.:Harry S. Truman (1945–53).\n'}]}]