The correct answer is: A. POP3
POP3 (Post Office Protocol version 3) is a standard Internet protocol that allows users to retrieve email from a remote server. It is a simple, text-based protocol that is supported by most email clients.
FTP (File Transfer Protocol) is a standard Internet protocol that allows users to transfer files between two computers. It is a more complex protocol than POP3 and is not typically used for email retrieval.
MAP (Mail Access Protocol) is a proprietary protocol developed by Microsoft for accessing email from Exchange Server. It is not a standard protocol and is not supported by most email clients.
Therefore, the only protocol that allows a user to retrieve her/his mail from the mail server to her/his mail reader is POP3.