Final answer:
The strongest form of authentication is using both a password and a device with changing unique numbers, known as two-factor authentication, which heightens security by requiring two distinct forms of identification.
Step-by-step explanation:
The strongest example of authentication from the options provided is e. Using both a password and a device with changing unique numbers, which is known as two-factor authentication (2FA). This method provides enhanced security because it requires two different forms of verification: something you know (your password) and something you have (a device generating unique codes, often a smartphone).
Two-factor authentication makes it much harder for unauthorized users to access your account since even if they obtain your password, they still need access to the second factor. A password alone, even memorized or encrypted, does not offer the same level of security because it is still a single factor and can be compromised. Therefore, the combination of a password with a device that provides a one-time code is considered the most robust form of authentication listed.