Final answer:
The Big SQL authentication mode utilizing secret-key cryptography for strong client/server application security is Kerberos Authentication.
Step-by-step explanation:
The Big SQL authentication mode designed to provide strong authentication for client/server applications by using secret-key cryptography is B) Kerberos Authentication. Kerberos is a network authentication protocol that works on the principle of tickets to allow nodes to prove their identity securely over a non-secure network. It is widely accepted for its ability to provide robust security through the use of secret-key cryptography, which provides mutual authentication—both the user and the service verify each other's identity. Other modes like LDAP Authentication are more about directory services, Password Authentication is a basic form, and No Authentication means security is not enforced..