Back is related to Exchange. Exchange is related to Trading. 
you are likely to find Door in/at/on School. you are likely to find Door in/at/on Office. Office is related to Working. Working is related to Busy. 
Back <--RelatedTo--> Exchange <--RelatedTo--> Trading 
School <--AtLocation-- Door --AtLocation--> Office <--RelatedTo--> Working <--RelatedTo--> Busy 