Bob learned that his username and password for a popular game has been compromised. He contacts the company and resets all the information. The company suggests he use two-factor authentication; which

Two-factor authentication requires credentials from two different categories. A username and password represent 'something you know,' while a fingerprint scanner represents 'something you are' (biometric). Combining these two distinct factor categories is the definition of 2FA, making this the only option that qualifies.

A username and a stronger password are both 'something you know' - changing the strength does not add a second factor category.

A new username and password still represent only a single factor category ('something you know') and provide no additional authentication layer.

Using only a fingerprint scanner is single-factor authentication ('something you are') - removing the password eliminates a factor rather than adding one.