Fall is related to Apple. Apple is related to Teacher. Missionary is a type of Teacher. Missionary is a type of Worker. 
Obstacle is a synonym of Barrier. Barrier is a synonym of Fence. Fence is a synonym of Defend. 
Fall <--RelatedTo--> Apple <--RelatedTo--> Teacher <--IsA-- Missionary --IsA--> Worker 
Obstacle <--Synonym--> Barrier <--Synonym--> Fence <--Synonym--> Defend 