Question: what is the basis of china in claiming spratly islands
[{'answer': 'historical sovereignty of the islands', 'provenance': [{'wikipedia_id': '28336429', 'title': 'Spratly Islands dispute', 'start_paragraph_id': 4, 'start_character': 1105, 'end_paragraph_id': 4, 'end_character': 1142, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '28336429', 'title': 'Spratly Islands dispute', 'start_paragraph_id': 4, 'start_character': 0, 'end_paragraph_id': 4, 'end_character': 1328, 'bleu_score': 0.9902197551206561, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 15234914939556394553}, 'section': 'Section::::Abstract.'}]}]