Choose the correct response to show the friend's extreme surprise and disbelief.

Arthur: "I accidentally bought a haunted castle in Scotland on the internet last night."
Friend: "___"

The correct answer is You bought a what?

This is an echo question. We use echo questions to show surprise or ask for repetition when we can't believe what we just heard! Instead of using normal question word order (like "What did you buy?"), we repeat the speaker's sentence and replace the surprising part with a question word, keeping the voice pitch high at the end.