hsiaoyunh“What if the speaker has already known that there are more than one eating his/her cake?
Is the question still the same as "Who is ..."?”
Yes. It's still
Who is ...?The choice between Who is/was ? and Who are/were ? is actually very simple.
Use Who are/were? only when a plural noun phrase follows. Otherwise, always use Who is/was ?
Who
are they? Who was talking about it? Who
were the first people to inhabit North America? Who was that? Who
are those men in the kitchen? Who's saying it's a lie? Who was giving you trouble about it? Who
were the guys who helped us that day? Who was singing in the hallway? Who
were the singers? Who is this I see before me? Who in the world
are these interns you're talking about?
CJ