20331
In contrast , the friction of graphene folded onto bulk - like graphene was indistinguishable from that of mono - layer graphene on SiO2 despite the ultra - smoothness of bulk - like graphene .
 Chemical: graphene; Chemical: graphene; Chemical: graphene; Chemical: SiO2; Chemical: graphene
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: graphene, graphene, graphene, SiO2, graphene 
Answer:
 Chemical: graphene; Chemical: graphene; Chemical: graphene; Chemical: SiO2; Chemical: graphene