Question: where are calcium ions stored in a cell
[{'answer': 'mitochondria', 'provenance': [{'wikipedia_id': '378744', 'title': 'Calcium in biology', 'start_paragraph_id': 3, 'start_character': 166, 'end_paragraph_id': 3, 'end_character': 178, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'endoplasmic reticulum', 'provenance': [{'wikipedia_id': '378744', 'title': 'Calcium in biology', 'start_paragraph_id': 3, 'start_character': 187, 'end_paragraph_id': 3, 'end_character': 208, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}]