Mechanism is related to Stair. Stair is related to Hallway. Floor is part of Hallway. Floor is related to Drop. 
Single is related to Chair. Chair is a synonym of Moderate. Moderate is related to Mild. 
Mechanism <--RelatedTo--> Stair <--RelatedTo--> Hallway <--PartOf-- Floor <--RelatedTo--> Drop 
Single <--RelatedTo--> Chair <--Synonym--> Moderate <--RelatedTo--> Mild 