System is a synonym of Complex. Complex is a synonym of Hard. Hard is the opposite of Simple. 
Check is a type of Change. Pain can cause/lead to Change. Pain is related to Hunger. Hunger is related to Feeling. 
System <--Synonym--> Complex <--Synonym--> Hard <--Antonym--> Simple 
Check --IsA--> Change <--Causes-- Pain <--RelatedTo--> Hunger <--RelatedTo--> Feeling 