Cultural is related to Music. Music is the opposite of Secular. Secular is the opposite of Regular. Regular is related to Grade. 
Offer is related to Opportunity. Opportunity is a synonym of Chance. Happen is a type of Chance. Happen is related to Could. 
Cultural <--RelatedTo--> Music <--Antonym--> Secular <--Antonym--> Regular <--RelatedTo--> Grade 
Offer <--RelatedTo--> Opportunity <--Synonym--> Chance <--IsA-- Happen <--RelatedTo--> Could 