Final answer:
Two-factor authentication (2FA) requires two types of identification, and an example is a password paired with a security token. This provides enhanced security by combining something you know with something you have.
Step-by-step explanation:
The concept in question is known as two-factor authentication (2FA), which is an additional security process to secure accounts beyond just a password. In two-factor authentication, the user is required to provide two different forms of identification before accessing their account.
An example of two-factor authentication is: c. password and token. This combination typically involves something you know (a password) and something you have (a security token). A token can be a physical device that generates a one-time passcode or a software-based token that creates a code that changes after a set period of time.
Other forms, such as a fingerprint and retinal scan, represent two forms of biometric identification, which may be used in multi-factor authentication but are not a combination of two different factors (as they both represent something you are).
Therefore, the correct option is c, which pairs a knowledge factor (password) with a possession factor (token).