Drive is related to Motivate. Fear can Motivate. Fear is related to Serious. 
Defensive is related to Tower. you are likely to find Tower in/at/on Airport. you are likely to find Clerk in/at/on Airport. 
Drive <--RelatedTo--> Motivate <--CapableOf-- Fear <--RelatedTo--> Serious 
Defensive <--RelatedTo--> Tower --AtLocation--> Airport <--AtLocation-- Clerk 