Final answer:
The command to configure a clear-text password for enable mode is 'enable password'. This method is not secure, and 'enable secret' command should be used instead for encryption. Options 'password 7' and 'service password-encryption' have different uses and do not set enable mode passwords.
Step-by-step explanation:
The command used to configure a clear-text password for gaining access to enable mode on a device, such as a router or switch in a Cisco IOS environment, is d) enable password.
To set this password, you would enter global configuration mode and issue the command enable password followed by the password you desire.
It's important to note that this method stores the password in clear-text in the device's configuration file, which is not secure. For enhanced security, the enable secret command is preferred, as it encrypts the password.
The option password 7 typically refers to a type-7 encrypted password seen in configuration files, not a command. The service password-encryption command enables obfuscation of clear-text passwords in configuration files, but it's not considered secure encryption.