A smart card provides an additional factor of authentication by storing secure credentials, such as certificates, that cannot be guessed or replicated. It complements user accounts and is "something you have".
* Why Not A (Fingerprint reader): This is "something you are", but the scenario specifically requires a physical token.
* Why Not C (Secure token): Secure tokens are also valid but may not integrate as seamlessly into multi- factor authentication for physical and system access.
* Why Not D (NFC scanner): An NFC scanner is a device and not a token itself; it reads cards or other credentials.
CompTIA A+ Exam Reference: Core 2 (220-1102), Section 2.5, access controls.