Breathing can be used for Survival. Thinking can be used for Survival. Writing can cause/lead to Thinking. Writing is a synonym of Document. 
Hard is related to Ice. Ice is related to Cake. Cake is related to Anniversary. Anniversary is related to Age. 
Breathing --UsedFor--> Survival <--UsedFor-- Thinking <--Causes-- Writing <--Synonym--> Document 
Hard <--RelatedTo--> Ice <--RelatedTo--> Cake <--RelatedTo--> Anniversary <--RelatedTo--> Age 