I am employed by the company Foo and work as a subcontractor for a consultant company Bar at the customer company Qux.How should I answer How do you know NameOfPerson? at LinkedIn when I add:a person who is employed at Qux.a person who is employed by another consultant company.a person who we (at Foo) hired as a consultant and worked with me for a while.a teacher I had at the University who knows me but wasnt really a (real) friend.In the list of answers I have:ColleagueClassmateWeve done business togetherFriendOtherI dont know NameOfPersonIn the colleague section, I only have the places where I have worked listed. As I am a consultant maybe there is a way to add the customers Ive worked with? 
How to answer the How do you know question at LinkedIn for a couple of scenarios?
linkedin