Economics is etymologically related to Economy. Economics is related to Supply. 
you are likely to find Class in/at/on Conference. Class is related to Subject. Subject is related to Investigation. Examination is a type of Investigation. 
Economy <--EtymologicallyRelatedTo-- Economics <--RelatedTo--> Supply 
Conference <--AtLocation-- Class <--RelatedTo--> Subject <--RelatedTo--> Investigation <--IsA-- Examination 