Question: when was the last time tug-of-war was an official olympic sport
[{'answer': '1920', 'provenance': [{'wikipedia_id': '3795330', 'title': 'Tug of war at the Summer Olympics', 'start_paragraph_id': 1, 'start_character': 95, 'end_paragraph_id': 1, 'end_character': 99, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '3795330', 'title': 'Tug of war at the Summer Olympics', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 508, 'bleu_score': 0.978375183951072, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3309199993839209238}, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '3795330', 'title': 'Tug of war at the Summer Olympics', 'section': 'Section::::Abstract.', 'start_paragraph_id': 1, 'end_paragraph_id': 1, 'meta': {'evidence_span': ['Tug of war was contested as a team event in the Summer Olympics at every Olympiad from 1900 to 1920', 'Tug of war was contested as a team event in the Summer Olympics at every Olympiad from 1900 to 1920.', 'Tug of war was contested as a team event in the Summer Olympics at every Olympiad from 1900 to 1920.']}}]}, {'provenance': [{'wikipedia_id': '7377620', 'title': 'United States at the 1920 Summer Olympics', 'section': 'Section::::Tug of war.\n', 'start_paragraph_id': 67, 'end_paragraph_id': 67, 'meta': {'evidence_span': ["The Americans joined the British in tying Sweden's mark for most appearances in the short life of tug of war at the Olympics at three of five. The Bergvall System was used in 1920.", 'The United States competed in the Olympic tug of war tournament for the third time in 1920']}}]}]