The correct answer is (d) SMTP.
SMTP stands for Simple Mail Transfer Protocol. It is a standard Internet protocol for electronic mail (email) transmission. SMTP is an application-layer protocol that uses TCP/IP to send email messages from an email client to an email server, or from one email server to another.
FTP stands for File Transfer Protocol. It is a standard network protocol used to transfer files from one host to another host over a TCP/IP network. FTP is a client-server protocol, which means that there are two programs involved in the transfer: a client program on the user’s computer and a server program on the remote computer.
RPC stands for Remote Procedure Call. It is a protocol that allows a program on one computer to call a procedure on another computer. RPC is used to implement distributed computing, where multiple computers cooperate to perform a task.
SNTP stands for Simple Network Time Protocol. It is a protocol used to synchronize the clocks of computer systems over a network. SNTP is a client-server protocol, which means that there are two programs involved in the synchronization: a client program on the user’s computer and a server program on the remote computer.