Which of the following provides secure, remote shell access to a system?

The choice that provides secure, remote shell access to a system is SSH, which stands for Secure Shell. SSH is a protocol that allows users to securely log into another computer over a network, providing a text-based interface to execute commands. It incorporates strong encryption methods to protect the data being transmitted over the connection, ensuring that sensitive information such as usernames and passwords cannot be intercepted by attackers during transmission.

In contrast, Remote Desktop is designed for graphical user interfaces, allowing users to view and interact with the desktop of a remote machine but does not focus specifically on shell access. Telnet is another protocol that can provide remote access but does so without encryption, making it vulnerable to eavesdropping and other attacks. FTP, or File Transfer Protocol, is solely used for transferring files between systems and does not offer shell access at all. Thus, SSH is the preferred method for secure command-line access to remote systems.