Which of the following is an example of two factor authentication?

A PIN and a birth date are both 'something you know' factors, placing them in the same authentication category and making this single-factor authentication.

A username and password are both 'something you know' factors and represent a single authentication factor, not two-factor authentication.

A digital certificate and a hardware token are both classified under 'something you have', meaning they belong to the same factor category and do not constitute true two-factor authentication.

A fingerprint belongs to the 'something you are' category (biometric), while a smartcard ID belongs to the 'something you have' category (physical token). Because these two credentials come from different authentication factor categories, combining them satisfies the requirement for two-factor authentication.