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PET probe discovery using in situ click chemistry uses ( 19 ) F - bearing fragments as ( 18 ) F surrogates .
 Chemical: ( 19 ) F; Chemical: ( 18 ) F
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: ( 19 ) F, ( 18 ) F 
Answer:
 Chemical: ( 19 ) F; Chemical: ( 18 ) F