7.3.2 Wh-movement
B’s response involves what is known as an echo question, in which a previously uttered sentence is more or less repeated and a part of it that was either not heard or not believed replaced by a wh-element. The meaning is quite clear: it is a request for someone to repeat or confirm the previous statement. This is very different from the meaning of a wh-question which is asking for information about a particular aspect of the sentence. Compare: