Comprehensive and Detailed Explanation From Exact Extract:

Multi-Factor Authentication (MFA) requires at least two different types of authentication factors:

Something you know (e.g., password or PIN)

Something you have (e.g., smartphone or hardware token)

Something you are (e.g., fingerprint or facial recognition)

Option A, sending a code to the user’s phone, is an example of " something you have " — a physical device that receives a one-time passcode. Combined with a password, this forms a proper MFA implementation.

B. Date of birth is another knowledge-based factor (like a password), not a second factor type.

C. Solving a math problem is not a recognized authentication factor.

D. A PIN is also " something you know " and does not count as a distinct MFA factor when paired with a password.