27096
The focus of this study is to obtain a microscopic understanding of the role of subsurface hydrogen in enhancing the associative desorption of molecular hydrogen .
 Chemical: hydrogen; Chemical: hydrogen
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: hydrogen, hydrogen 
Answer:
 Chemical: hydrogen; Chemical: hydrogen