Theme is related to Ride. Ride is a type of Lie. Lie is related to Boast. 
Could is the opposite of Would. Would is related to Possible. Possible is related to Bull. 
Theme <--RelatedTo--> Ride --IsA--> Lie <--RelatedTo--> Boast 
Could <--Antonym--> Would <--RelatedTo--> Possible <--RelatedTo--> Bull 