23247
Exact calculations of relaxation times under MAS provide a simple and robust means to test motional models in cases where relaxation rate maxima are observed , including for systems where the crystal structure of the material is unknown .
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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:  
Answer:
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