At the Transfiguration, the apostles seemed to know that the persons conversing with Jesus were Moses and Elijah. How?

The Gospels do not explain how the disciples were able to recognize Moses and Elijah at the Transfiguration, so any answer is a guess.

Possible ways the disciples were able to recognize Moses and Elijah:

• Jesus referred to them by name in his conversation with them, and the disciples overheard it.
• The disciples overheard the conversation, and the context informed them with whom Jesus was speaking.
• They had something unique about their appearance that made them readily recognizable (Exodus 34:29; 2 Kings 1:8).
• There was some sort of heavenly announcement that wasn’t recorded in the Gospels.
• Jesus explained to the disciples who they were.
• They were divinely inspired to recognize them, similar to God’s revelation to Peter that Jesus is the messiah.