Which protocol is essential for facilitating file transfers over a network?

The answer is B, as FTP (File Transfer Protocol) is specifically designed for transferring files over a network. It supports various features such as allowing users to upload and download files, manage directories, and transfer files in both binary and ASCII formats. FTP operates over TCP/IP, which provides the foundational communication protocols for the internet but does not directly handle file transfers itself.

The other options, while related to network communications, serve different purposes. HTTP (Hypertext Transfer Protocol) is primarily used for transmitting web pages. SMTP (Simple Mail Transfer Protocol) is utilized for sending emails, and although TCP/IP is crucial for data transmission across networks, it is not a protocol dedicated specifically to file transfers. Thus, FTP stands out as the correct answer for facilitating file transfers.