Question: when did the us leave the vietnam war
[{'answer': '1970', 'provenance': [{'wikipedia_id': '32611', 'title': 'Vietnam War', 'start_paragraph_id': 6, 'start_character': 1061, 'end_paragraph_id': 6, 'end_character': 1065, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '32611', 'title': 'Vietnam War', 'start_paragraph_id': 106, 'start_character': 0, 'end_paragraph_id': 106, 'end_character': 1438, 'bleu_score': 0.7964908970805791, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3224199363798928236}, 'section': 'Section::::Nixon Doctrine and Vietnamization, 1969–72.:ARVN taking the lead and U.S. ground-force withdrawal.\n'}]}]