Question: when is mass conserved according to the law of conservation of mass
[{'answer': 'over time', 'provenance': [{'wikipedia_id': '145040', 'title': 'Conservation of mass', 'start_paragraph_id': 1, 'start_character': 183, 'end_paragraph_id': 1, 'end_character': 192, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '145040', 'title': 'Conservation of mass', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 325, 'bleu_score': 0.8957637419652761, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 6492940289445647563}, 'section': 'Section::::Abstract.'}]}]