Gas is related to Pump. Pump is related to Air. Air is related to Roll. Roll is related to Genre. 
Mention is related to Say. Say is related to Describe. Describe is related to Illustrate. 
Gas <--RelatedTo--> Pump <--RelatedTo--> Air <--RelatedTo--> Roll <--RelatedTo--> Genre 
Mention <--RelatedTo--> Say <--RelatedTo--> Describe <--RelatedTo--> Illustrate 