You probably know from the forum guidelines that you are expected to tell us your own thoughts about coursework, not just to ask "which is right?" What do you think about this question? It comes down to when "who?" is seen as singular or plural.
I do agree with you. I think it depends on "who"; but the sentence in the exercise is just an independent sentence, there's no context given. So, can both "is" and "are" be considered as correct? Thank you!