Prompt is a synonym of Motivate. Motivate is a type of Cause. Occasion is a type of Cause. Occasion is related to Oak. 
Excuse is a synonym of Account. Account is a synonym of Calculate. Machine can be used for Calculate. Machine can be used for Dig. 
Prompt <--Synonym--> Motivate --IsA--> Cause <--IsA-- Occasion <--RelatedTo--> Oak 
Excuse <--Synonym--> Account <--Synonym--> Calculate <--UsedFor-- Machine --UsedFor--> Dig 