Single sign-on (SSO) is the correct answer because it allows users to authenticate once and access multiple systems without the need to sign in multiple times. This increases efficiency and enhances the user experience by reducing the number of credentials users must remember and enter. On the other hand, Multifactor authentication adds an extra layer of security by requiring two or more authentication methods, which is unrelated to the convenience of single sign-on. Terminal Access Controller Access-Control System Plus (TACACS+) is a network protocol that provides centralized authentication for users who are attempting to gain access to a network system, but it does not enable access to multiple systems with a single login session. Remote Authentication Dial-in User Service (RADIUS) is another authentication protocol used to manage network access, but like TACACS+, it is not specifically focused on single sign-on functionality.