Fuel is related to Oil. you are likely to find Oil in/at/on Kitchen. you are likely to find Pie in/at/on Kitchen. 
Could is etymologically related to Should. Should is related to Ought. Ought is a form of Owe. 
Fuel <--RelatedTo--> Oil --AtLocation--> Kitchen <--AtLocation-- Pie 
Could --EtymologicallyRelatedTo--> Should <--RelatedTo--> Ought --FormOf--> Owe 