Question: which is a metric unit of amount of a pure substance
[{'answer': 'the mole', 'provenance': [{'wikipedia_id': '759264', 'title': 'Amount of substance', 'start_paragraph_id': 18, 'start_character': 32, 'end_paragraph_id': 18, 'end_character': 40, 'bleu_score': 1.0, 'section': 'Section::::Derived quantities.:Amount concentration (moles per liter).\n'}]}]