Question: where did copper come from for bronze age
[{'answer': "the Earth 's crust", 'provenance': [{'wikipedia_id': '25941423', 'title': 'Tin sources and trade in ancient times', 'start_paragraph_id': 1, 'start_character': 249, 'end_paragraph_id': 1, 'end_character': 267, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '25941423', 'title': 'Tin sources and trade in ancient times', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 604, 'bleu_score': 0.9059742337612021, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 13683476709578945538}, 'section': 'Section::::Abstract.'}]}]