Which is not an internet protocol?

The correct answer is C. STP.

• HTTP (Hypertext Transfer Protocol) is an application-layer protocol that defines how messages are formatted and transmitted between a web server and a web browser.
• FTP (File Transfer Protocol) is a standard network protocol used to transfer files from one host to another host over a TCP/IP network.
• IP (Internet Protocol) is a network protocol that governs the format of data sent over the Internet.
• STP (Spanning Tree Protocol) is a network protocol that prevents network loops in a switched network.

STP is not an internet protocol because it is used to prevent network loops in a switched network, not to transfer data over the Internet.