Different internet services are optimised for different jobs, so the best choice depends on what "transfer a large file" specifically demands: reliability, efficiency, and the ability to move big blocks of data directly between machines.

File Transfer Protocol (FTP) is a standard network protocol designed precisely for uploading and downloading files between a client and a server over a TCP/IP network. It handles large files efficiently, supports resuming interrupted transfers, and is the purpose-built service for this task.

Why the others are less suitable:

• World Wide Web is a system of interlinked hypertext pages for browsing and viewing information, not a dedicated file-transfer service.
• E-mail can carry attachments, but mail servers usually cap attachment size (often around 20–25 MB), so it is unreliable for genuinely large files.
• Instant Messaging is built for quick, real-time text conversation and typically imposes tight limits on file size.

Because FTP is the service specifically engineered for moving large files, the correct answer is File Transfer Protocol (FTP).