Answer: a) Improving authentication efficiency
c) Reducing traffic on the WAN
Explanation: Multiple sites are more than one domain used for increasing the service by spreading through various page of sites in large networks. It helps in elimination of the traffic in wide area network(WAN) and also has the enhances the authentication of the network and service.
Other options are incorrect because replication of the services are not quick and do not persist single IP subnet. Thus, the correct options are (a) and (c).