What line in the /etc/pam.d/su file will allow root to use su without supplying passwords?

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 supplying passwords?

A.
auth required pam_norootpw.so

B.
auth sufficient pam_norootpw.so

C.
auth required pam_rootok.so

D.
auth sufficient pam_rootok.so