This is a plural/singular verb question, but I can't see it answered elsewhere.

Elsewhere the consensus is that when you have a collective noun and plural nouns, you can use either a singular or plural verb eg

A pack of wolves was attacking the sheep or
A pack of wolves were attacking the sheep

But what about a sentence like:

Which of you two boys is/are throwing stones at the cat.

Can you use either "is" or "are"?