Final answer:
The correct option is 'frequently used' because passwords are a common part of daily digital life. So, option C is correct.
Step-by-step explanation:
In addressing whether a password is a. always secure, b. always memorable, c. frequently used, or d. always mnemonic, it's important to understand the nature of passwords. Passwords are meant to provide security but are not inherently secure; their strength depends on their complexity and how they are used. While a password may be frequently used, this does not inherently make it secure. Ideally, a password should be memorable to the user to prevent frequent resets, but this is not always the case. Finally, passwords are sometimes mnemonic, as in the case where a user creates a password based on a memorable pattern or phrase, but this also is not always true.
While passwords are a fundamental part of digital security, they vary greatly in their memorability, mnemonic nature, and security. The use of mnemonic devices, such as acronyms or acrostics, can help in creating passwords that are both secure and easier to remember. This can assist in ensuring that a frequently used password is also a strong line of defense against unauthorized access. So, the correct option is frequently used, because people will often use passwords for various accounts and applications multiple times a day, making them a common part of daily digital life. However, it's crucial to pair frequent use with strong security measures.