The Crossover Error Rate (CER) is a good measure of performance for:

CER specifically measures the point where the False Acceptance Rate (FAR) and False Rejection Rate (FRR) of a biometric system are equal, providing a balanced indicator of its effectiveness.

Tokens are physical or digital devices used for authentication and do not have performance metrics like CER, which is specific to biometric matching.

Kerberos is a network authentication protocol that uses tickets, and its performance is measured by factors like latency or throughput, not error rates related to biometric scans.

While a fingerprint scan is a biometric method, 'Biometrics' (choice A) is the broader and more accurate category for which CER is a general performance measure.

Discretionary access control (DAC) is an authorization model where resource owners control access, and its performance is not evaluated using biometric error rates.