19399
Synthetically tractable click hydrogels for three - dimensional cell culture formed using tetrazine - norbornene chemistry .
 Chemical: tetrazine; Chemical: norbornene
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: tetrazine, norbornene 
Answer:
 Chemical: tetrazine; Chemical: norbornene