Physical Characteristics for User Identity Verification

C.

The correct answer is C. Biometrics.

Biometrics is a type of authentication that relies on a physical characteristic of the user to verify their identity. This can include fingerprints, facial recognition, iris scans, and other physical attributes that are unique to an individual. Biometric authentication is a highly secure form of authentication since it is difficult for someone to fake or steal another person's biometric data.

Social engineering is a type of attack that relies on manipulating people into revealing confidential information or performing actions that compromise security. It is not an authentication mechanism.

Kerberos v5 is a network authentication protocol that uses cryptography to authenticate users and systems on a network. It does not rely on physical characteristics of the user.

CHAP (Challenge-Handshake Authentication Protocol) is a protocol used to authenticate a user or network node to another node in a network. It uses a shared secret and does not rely on physical characteristics of the user.

In summary, biometrics is the only option among the given choices that relies on a physical characteristic of the user to verify identity.