Question: name the shellfish which is cultured to obtain pearl
[{'answer': 'oyster', 'provenance': [{'wikipedia_id': '1140443', 'title': 'Cultured pearl', 'start_paragraph_id': 1, 'start_character': 58, 'end_paragraph_id': 1, 'end_character': 64, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'the freshwater river mussels , and the saltwater pearl oysters'}, {'provenance': [{'wikipedia_id': '1140443', 'title': 'Cultured pearl', 'start_paragraph_id': 1, 'start_character': 2, 'end_paragraph_id': 1, 'end_character': 244, 'bleu_score': 0.8536608424631631, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 13166137613989133865}, 'section': 'Section::::Abstract.'}]}]