Question: when did north and south vietnam become one country
[{'answer': '1975', 'provenance': [{'wikipedia_id': '10135916', 'title': 'Northern, central and southern Vietnam', 'start_paragraph_id': 20, 'start_character': 13, 'end_paragraph_id': 20, 'end_character': 17, 'bleu_score': 1.0, 'section': 'Section::::Historical context.\n'}]}, {'provenance': [{'wikipedia_id': '10135916', 'title': 'Northern, central and southern Vietnam', 'start_paragraph_id': 20, 'start_character': 0, 'end_paragraph_id': 20, 'end_character': 566, 'bleu_score': 0.950027409461844, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 16111985601824381929}, 'section': 'Section::::Historical context.\n'}]}]