Users with the ACCOUNTADMIN role can perform several operations on existing users, which include the ability to SHOW users, DESCRIBE a given user, ALTER user settings, or DROP a user. The correct operations are aligned with showing, describing, altering, and dropping users, but not defining, deleting, or modifying users in a way not covered by the listed commands. Hence, the option that correctly lists the commands executable on existing users by the ACCOUNTADMIN role is SHOW users, DESCRIBE a given user, ALTER, or DROP a user.