8034
Several enzymes and synthetic bioinorganic systems perform the activation of C - H bonds in methane and small hydrocarbons , mediated by transition metal mononuclear centers .
 C - H, methane, hydrocarbons, transition metal
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 C - H, methane, hydrocarbons, transition metal