Main is related to State. Office is a type of State. you are likely to find Pencil in/at/on Office. Pencil entails/necessarily involves Trace. 
Nail is related to Wood. Wood is related to Natural. Natural is a synonym of Biological. 
Main <--RelatedTo--> State <--IsA-- Office <--AtLocation-- Pencil --Entails--> Trace 
Nail <--RelatedTo--> Wood <--RelatedTo--> Natural <--Synonym--> Biological 