Question: what metric unit is used to describe the mass of an object
[{'answer': 'kilogram', 'provenance': [{'wikipedia_id': '19048', 'title': 'Mass', 'start_paragraph_id': 2, 'start_character': 33, 'end_paragraph_id': 2, 'end_character': 41, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '19048', 'title': 'Mass', 'start_paragraph_id': 2, 'start_character': 0, 'end_paragraph_id': 2, 'end_character': 506, 'bleu_score': 0.6703021105036181, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15767583551805016717}, 'section': 'Section::::Abstract.'}]}]