Question: when did the united states start trading with china
[{'answer': '1845', 'provenance': [{'wikipedia_id': '277880', 'title': 'China–United States relations', 'start_paragraph_id': 6, 'start_character': 67, 'end_paragraph_id': 6, 'end_character': 71, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]