Aggressive is related to War. you are likely to find Confusion in/at/on War. 
Metal is the opposite of Plastic. Plastic can be Solid. Piano can be Solid. Piano is related to Instrument. 
Aggressive <--RelatedTo--> War <--AtLocation-- Confusion 
Metal <--Antonym--> Plastic --HasProperty--> Solid <--HasProperty-- Piano <--RelatedTo--> Instrument 