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Polysialic acid ( polySia ) is a large , cell - surface linear homopolymer composed of alpha 2 , 8 - linked sialic acid residues .
 Chemical: sialic acid
Given options, please tell me the categories of all the listed entity words.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
 Entities: sialic acid 
Answer:
 Chemical: sialic acid