Question: what does hg stand for in metric system
[{'answer': 'Inch of mercury', 'provenance': [{'wikipedia_id': '2319766', 'title': 'Inch of mercury', 'start_paragraph_id': 0, 'start_character': 0, 'end_paragraph_id': 0, 'end_character': 15, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '2319766', 'title': 'Inch of mercury', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 178, 'bleu_score': 0.934334813046729, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 13083253259141914211}, 'section': 'Section::::Abstract.'}]}]