Used as subject when asking about which person or people.
I.e. Who is responsible for advertising?
– It’s Mr. Temba.
Used as object when asking which person or people.
I.e. Whom are you suing for sexual harassment?
– I’m suing my own boss.
Used, in wide choice, to ask about things.
I.e. What is the problem with this electrical good?
– The customers think it is old-fashioned.
Used, in limited choice, to ask about things or people.
I.e. Which dress is cheaper?
– The white dress is cheaper than the red one.