4939
O2 - independent formation of the inactive states of NiFe hydrogenase .
 Chemical: O2; Chemical: NiFe
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: O2, NiFe 
Answer:
 Chemical: O2; Chemical: NiFe