"Are you at the restaurant?"
There are two kinds of being verbs in Italian, and they refer to differ types of being: one being more permanent (the sei) and other having to do with less permanent things (the stai). A place of origin (I am from...) would use sei, while temporary location (I am at such and such a place right now) would use stai.
What? "al" means "at the"? They never told me that... Good thing it was multiple-choice.
I'm not 100% sure, but I think that would translate to "Is that you at the restaurant?"
Because this is the english way to formulate a question. In Italian or portuguese we don't change the phrase only the intonation of it.
That's not entirely true. In most questions in Italian the pronoun does move to the end of the phrase. So it would be "Sei al ristorante tu?" But only if you wanted to emphasize you. As in, "are YOU at the restaurant?"
Hmmm... I think "c'è.." means "there is...", so it does not really work here. I have been known to make mistakes though.