Answer Description

SFTP (SSH File Transfer Protocol) is a protocol for securely uploading files to a remote server. SSH alone is not enough to upload a file and is incorrect. SSH provides the encryption & authentication but does not meet the requirement to upload a file. As SFTP builds upon SSH with functionality for file upload it is the correct answer.

Wikipedia

In computing, the SSH File Transfer Protocol (also known as Secure File Transfer Protocol or SFTP) is a network protocol that provides file access, file transfer, and file management over any reliable data stream. It was designed by the Internet Engineering Task Force (IETF) as an extension of the Secure Shell protocol (SSH) version 2.0 to provide secure file transfer capabilities. The IETF Internet Draft states that, even though this protocol is described in the context of the SSH-2 protocol, it could be used in a number of different applications, such as secure file transfer over Transport Layer Security (TLS) and transfer of management information in VPN applications. This protocol assumes that it is run over a secure channel, such as SSH, that the server has already authenticated the client, and that the identity of the client user is available to the protocol.