10579
The changes observed in the chemical shifts of ( 31 ) P MAS NMR spectra with x are found to be too large to be caused solely by changing sodium modification of the phosphate SRO structural groups , and this indicates that internetwork bonding between phosphorus and boron through bridging oxygens ( BOs ) , P - O - B , must be a major contributor to the IRO structure of these glasses .
 ( 31 ) P, sodium, phosphorus, boron, oxygens, P - O - B
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 ( 31 ) P, sodium, phosphorus, boron, oxygens, P - O - B