Hard is related to Description. Description is a synonym of Variety. Variety is related to Old. Old is related to Must. 
Race is related to Speed. Speed is related to Drop. Drop is related to Reference. 
Hard <--RelatedTo--> Description <--Synonym--> Variety <--RelatedTo--> Old <--RelatedTo--> Must 
Race <--RelatedTo--> Speed <--RelatedTo--> Drop <--RelatedTo--> Reference 