To restrict user authentication to ONLY users who belong to a specific organizational unit, which file should be modified?

To restrict user authentication to ONLY users who belong to a specific organizational unit, which file should be modified?

A.
/etc/pam.d/ldap

B.
pam_ldap.conf

C.
/etc/pam.d/login

D.
ldap.conf

E.
pam.conf