Question: when did the bronze age start in china
[{'answer': 'about 2000 BC', 'provenance': [{'wikipedia_id': '4620', 'title': 'Bronze Age', 'start_paragraph_id': 51, 'start_character': 344, 'end_paragraph_id': 51, 'end_character': 357, 'bleu_score': 1.0, 'section': 'Section::::History.:Asia.:East Asia.:China.\n'}]}, {'provenance': [{'wikipedia_id': '4620', 'title': 'Bronze Age', 'start_paragraph_id': 51, 'start_character': 0, 'end_paragraph_id': 51, 'end_character': 479, 'bleu_score': 0.8523325711375941, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 1103518446663624347}, 'section': 'Section::::History.:Asia.:East Asia.:China.\n'}]}]