Introduction is part of Address. Address is related to Envelope. Envelope is related to Invitation. Invitation is related to Party. 
Correct is related to Real. Real is a type of Coin. Coin is related to Metal. Metal is related to Sheet. 
Introduction --PartOf--> Address <--RelatedTo--> Envelope <--RelatedTo--> Invitation <--RelatedTo--> Party 
Correct <--RelatedTo--> Real --IsA--> Coin <--RelatedTo--> Metal <--RelatedTo--> Sheet 