Poll: It is you who _____ eaten all the food.

mohd

I need to know the reason of choosing "have" or other choices.

Aiwendil

The verb must agree with 'who', obviously. 'Who' can be singular or plural ('who is he?' 'who are they?'). In this case, the number of 'who' must agree with the number of 'you'. And 'you' is grammatically plural (even though we use it for the logically singular 2nd person in place of the archaic 'thou'). Therefore, it must be 'have'. That's my reasoning, anyway.

dfbird

Get a grip, quiz takers. It depends on whether 'you' refers to one, or more than one person. In the southern US, you have y'all. Otherwise, you refers to both cases.

Nick

It depends on the context. Neither 'has' nor 'have' is correct without the context of singular or plural 'you'.