SSO can be implemented by using scripts that replay the users multiple log-ins against authentication servers to verify a user’s identity and to permit access to system services.
Single Sign on was the best answer in this case because it would include Kerberos.
When you have two good answers within the 4 choices presented you must select the BEST one. The high level choice is always the best. When one choice would include the other one that would be the best as well.
Reference(s) used for this question: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, 2001, John Wiley & Sons, Page 40.