Tough is a synonym of Hard. Hard is a synonym of Harsh. 
Select is related to Appoint. Appoint is related to Position. Landmark is a type of Position. Landmark is related to Statue. 
Tough <--Synonym--> Hard <--Synonym--> Harsh 
Select <--RelatedTo--> Appoint <--RelatedTo--> Position <--IsA-- Landmark <--RelatedTo--> Statue 