The correct answer is (b) SMTP.
SMTP stands for Simple Mail Transfer Protocol. It is a standard protocol for sending email messages between servers. SMTP is a text-based protocol, which means that it uses plain text to send and receive messages.
FTP stands for File Transfer Protocol. It is a standard protocol for transferring files between computers. FTP is a binary protocol, which means that it can transfer any type of file, including binary files.
SNMPP stands for Simple Network Management Protocol. It is a standard protocol for managing network devices. SNMPP is a management protocol, which means that it is used to monitor and control network devices.
RPCC stands for Remote Procedure Call Control. It is a standard protocol for calling procedures on remote machines. RPCC is a remote procedure call protocol, which means that it is used to call procedures on remote machines.
SMTP is the correct answer because it is the protocol that is used to transfer email messages from one machine to another.