Question: when did us troops start fighting in vietnam
[{'answer': '8 March 1965', 'provenance': [{'wikipedia_id': '32611', 'title': 'Vietnam War', 'start_paragraph_id': 73, 'start_character': 3, 'end_paragraph_id': 73, 'end_character': 15, 'bleu_score': 1.0, 'section': "Section::::Johnson's escalation, 1963–69.:American ground war.\n"}]}]