Question: when did the us join the allied forces in ww2
[{'answer': 'December 1941', 'provenance': [{'wikipedia_id': '4653534', 'title': 'Military history of the United States during World War II', 'start_paragraph_id': 9, 'start_character': 46, 'end_paragraph_id': 9, 'end_character': 59, 'bleu_score': 1.0, 'section': 'Section::::Origins.:American volunteers.\n'}]}]