Question: when did the washington post publish the pentagon papers
[{'answer': 'June 18 , 1971', 'provenance': [{'wikipedia_id': '230025', 'title': 'Pentagon Papers', 'start_paragraph_id': 47, 'start_character': 3, 'end_paragraph_id': 47, 'end_character': 17, 'bleu_score': 1.0, 'section': "Section::::Leak.:The Nixon administration's restraint of the media.\n"}]}, {'provenance': [{'wikipedia_id': '230025', 'title': 'Pentagon Papers', 'start_paragraph_id': 47, 'start_character': 0, 'end_paragraph_id': 47, 'end_character': 1038, 'bleu_score': 0.927778540361433, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 12615851965230032374}, 'section': "Section::::Leak.:The Nixon administration's restraint of the media.\n"}]}]