Which of the following is used to authenticate asymmetric keys?

A MAC address is a Layer 2 hardware identifier for a network interface card and has no role in cryptographic key authentication or PKI.

In a PKI, a certificate authority uses its own private key to digitally sign a certificate that contains the subject's public key - any party holding the CA's public key can verify the signature, confirming the asymmetric key is authentic and has not been tampered with, which is the foundational mechanism for trusting public keys.

A DMZ is a network architecture concept used to isolate exposed services from the internal network; it is unrelated to authenticating cryptographic keys.

Passwords are a shared-secret symmetric authentication method and cannot authenticate an asymmetric key pair, which requires a cryptographic binding mechanism such as a signed certificate.