Question: which heavy metal has highest concentration in earth's crust
[{'answer': 'iron', 'provenance': [{'wikipedia_id': '46659847', 'title': 'Heavy metals', 'start_paragraph_id': 2, 'start_character': 48, 'end_paragraph_id': 2, 'end_character': 52, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '46659847', 'title': 'Heavy metals', 'start_paragraph_id': 40, 'start_character': 0, 'end_paragraph_id': 40, 'end_character': 373, 'bleu_score': 0.9663744727315161, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15309229047500922943}, 'section': 'Section::::Formation, abundance, occurrence, and extraction.\n'}]}]