This passage is from my textbook:
We use have you? / isn't she? / do they? etc. to show interest in what somebody has said or to show surprise.
1): 'It rained every day during our holiday.' 'Did it? What a pity!'
2) 'Jim and Nora are getting married.' 'Are they? Really?'
As you see in those short statements of surprise the verb goes before the subject (Did it? Are they?) But in my real life experience I think I have always heard the subject before the verb (It did? They are?)
I can remember two situations:
'People are carnivores.' 'They are?' (conversation)
'George doesn't work, he is a bum. That's why he lives with us.' 'He does?' (Seinfeld show)
Best Answer
"Are they?" is the standard question form. In a question, we normally begin the sentence with an interrogative word like "where" or "how", or "is" or "are" or "do" or "does".
"They are?" is an example of a declarative statement turned into a question by simply putting a question mark at the end. In speech, it is intoned as a question, i.e. you raise the pitch of your voice at the end of the sentence. This is often done with more complex sentences, too.
For example, "I'm leaving XYZ Corporation." "What? You're going to quit your job?"
The idea is that you put a question mark at the end of a declarative sentence to express surprise or disbelief in the statement.