Prove is a synonym of Testify. Testify is a type of Inform. Teach is a type of Inform. Classroom can be used for Teach. 
Command is related to Must. Must is the opposite of Can. Drum is a type of Can. 
Prove <--Synonym--> Testify --IsA--> Inform <--IsA-- Teach <--UsedFor-- Classroom 
Command <--RelatedTo--> Must <--Antonym--> Can <--IsA-- Drum 