you would Buy because Have. Have is a synonym of Eat. Fruit can be used for Eat. Bean is a type of Fruit. 
Envelope is related to Mail. Mail is related to Reply. 
Buy --MotivatedByGoal--> Have <--Synonym--> Eat <--UsedFor-- Fruit <--IsA-- Bean 
Envelope <--RelatedTo--> Mail <--RelatedTo--> Reply 