Biological is the opposite of Adopt. Adopt is related to Related. Related is related to Metal. Metal is related to Precious. 
Free is related to Liberty. Liberty is a synonym of Privilege. Privilege is a synonym of Advantage. 
Biological <--Antonym--> Adopt <--RelatedTo--> Related <--RelatedTo--> Metal <--RelatedTo--> Precious 
Free <--RelatedTo--> Liberty <--Synonym--> Privilege <--Synonym--> Advantage 