What is the purpose of the nsswitch.conf file?

What is the purpose of the nsswitch.conf file?

A.
It is used to configure where the C library looks for system information such as host names and userpasswords.

B.
It is used to configure network protocol port numbers such as for HTTP or SMTP.

C.
It is used to configure LDAP authentication services for the local system.

D.
It is used to configure which network services will be turned on during the next system boot.