Guard is a type of Defender. Guard is related to Block. Block is related to Oil. Oil is related to Like. 
you are likely to find Bomb in/at/on Aircraft. Bomb is related to Terrorist. 
Defender <--IsA-- Guard <--RelatedTo--> Block <--RelatedTo--> Oil <--RelatedTo--> Like 
Aircraft <--AtLocation-- Bomb <--RelatedTo--> Terrorist 