14993
The role of osteoblasts ( OB ) in maintaining hematopoietic stem cells ( HSC ) in their niche is well elucidated , but the exact definition , both phenotypically and hierarchically of OB responsible for these functions is not clearly known .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
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