Environmental is related to Pollution. Pollution is related to Air. Air is a type of Mixture. Composition is a type of Mixture. 
History is related to Important. Important is similar to Historic. Historic is a synonym of Historical. 
Environmental <--RelatedTo--> Pollution <--RelatedTo--> Air --IsA--> Mixture <--IsA-- Composition 
History <--RelatedTo--> Important <--SimilarTo--> Historic <--Synonym--> Historical 