The best answer is A. Ensure the firewall data plane moves to fail-closed mode.

The key detail in this question is that the company prioritizes data confidentiality over transaction availability. In Security+ terms, when confidentiality is more important than keeping traffic flowing during a failure or security event, the preferred behavior is fail closed.

A fail-closed firewall blocks traffic if the device experiences a fault, failure, or security issue. This protects sensitive business data from being exposed or passed through an untrusted state. Even though this may interrupt business transactions, it aligns with the organization’s priority of protecting confidential information.

Why the other options are incorrect:

B. Implement a deny-all rule as the last firewall ACL rule.This is a standard firewall best practice, but it does not specifically address what should happen in case a security event occurs.

C. Prioritize business-critical application traffic through the firewall.This focuses on availability and performance, not confidentiality.

D. Configure rate limiting between the firewall interfaces.Rate limiting may help with traffic control or DoS reduction, but it does not best address the requirement to prioritize confidentiality during a security event.

From the SY0-701 perspective, when asked to choose between keeping systems available and preventing unauthorized access or data exposure, fail closed is the best security-focused answer.