Class is related to Unit. Troop is a type of Unit. Troop is a synonym of Parade. 
Trauma is a synonym of Injury. Injury is a synonym of Harm. Harm is the opposite of Heal. 
Class <--RelatedTo--> Unit <--IsA-- Troop <--Synonym--> Parade 
Trauma <--Synonym--> Injury <--Synonym--> Harm <--Antonym--> Heal 