Question: when did american troops first fight in ww1
[{'answer': 'October 21 , 1917', 'provenance': [{'wikipedia_id': '313147', 'title': 'American Expeditionary Forces', 'start_paragraph_id': 8, 'start_character': 148, 'end_paragraph_id': 8, 'end_character': 165, 'bleu_score': 1.0, 'section': 'Section::::Formation.\n'}]}, {'provenance': [{'wikipedia_id': '313147', 'title': 'American Expeditionary Forces', 'start_paragraph_id': 8, 'start_character': 0, 'end_paragraph_id': 8, 'end_character': 434, 'bleu_score': 0.972782728923768, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 8831506356944233340}, 'section': 'Section::::Formation.\n'}]}]