What will the man do with the letters?

The man will take the letters to the post office as this action typically involves delivering or mailing letters to their intended recipients. In many contexts, going to the post office signifies that the letters are ready to be sent. This choice reflects a standard practice for handling letters, particularly when someone is in possession of correspondence that needs to be dispatched.

Other scenarios, such as leaving them at home, giving them to a friend, or burning them, do not align with the common action associated with letters, which is to send them. The context of the question likely centers on the purpose of the letters, which is communication, achieved through mailing. Thus, taking them to the post office is the most logical and appropriate action in this situation.