Implement is related to Bell. Bell can be used for Toll. 
Wet is related to Cloud. Cloud is related to Source. Source is related to Fire. Trigger entails/necessarily involves Fire. 
Implement <--RelatedTo--> Bell --UsedFor--> Toll 
Wet <--RelatedTo--> Cloud <--RelatedTo--> Source <--RelatedTo--> Fire <--Entails-- Trigger 