Biometrics. Single sign-on means that you can use one type of authentication to get access to more than one system. While that could be going on in this scenario, it is not explicit, so biometrics is the more accurate answer. Multifactor means that more than one type of authentication is needed; for example, a fingerprint and a PIN. Let's say that users were expected to type a PIN into a keypad to gain access to the data center. You might find over time that some persons who enter don't match the owner of the PIN. That uncertainty can be avoided by incorporating biometrics. Tokens are used to gain access to systems and networks, and might include rolling one-time passwords, but do not incorporate a person's physical characteristics such as a fingerprint.