A user tries to log in to a system using ssh and receives this message: The authenticity of host ‘example-01 (1.2.3.4)’ can’t be established. RSA key fingerprint is 00:11:22:33:44:55:66:77:88:99:aa:bb:cc:dd:ee:ff. Are you sure you want to continue (yes/no)? Why is this message being generated?

A.
The user has never logged into example-01.

B.
The ssh-agent command is not running on the client machine.

C.
The user has entered an invalid password when trying to log into example-01.

D.
example-01 has changed its host key since the last time the user has logged into the system.