you are likely to find Sex in/at/on Bedroom. Bedroom is related to Sleep. Sleep is related to Camp. 
Essential is a synonym of Critical. Critical is a synonym of Vital. Vital is related to Necessary. 
Sex --AtLocation--> Bedroom <--RelatedTo--> Sleep <--RelatedTo--> Camp 
Essential <--Synonym--> Critical <--Synonym--> Vital <--RelatedTo--> Necessary 