On a new Linux system, the root user is being asked to provide the root user password before being able to use the su command. What line in the /etc/pam.d/su file will allow root to use su without…

`pam_norootpw.so` is not a standard or commonly used PAM module for this purpose, and `required` would still necessitate other authentication methods.

Similar to A, `pam_norootpw.so` is not the correct PAM module for this functionality.

While `pam_rootok.so` is the correct module, using `required` would mean that even if root is successfully authenticated by this module, other `required` or `requisite` modules in the stack would still need to succeed, potentially leading to a password prompt.

The `pam_rootok.so` module checks if the user is root (UID 0), and when combined with the `sufficient` control flag, it allows the root user to authenticate successfully without further authentication steps for `su`, bypassing the password prompt.