The best answer is C. Granting resource access after continuous validation.
Zero Trust architecture is based on the principle of never trust, always verify. Access should not be granted simply because a user or device is inside the network or was authenticated once earlier. Instead, access decisions should be based on continuous validation of identity, device health, context, and other relevant factors.
This means users and devices are evaluated repeatedly and granted only the minimum access necessary.
Why the other options are incorrect:
A). Building strong network boundaries to prevent intrusionThis reflects a traditional perimeter-based security model, not Zero Trust.
B). Verifying user identity once at the start of the sessionZero Trust does not rely on one-time authentication alone. It emphasizes ongoing verification.
D). Prioritizing perimeter defense to block external threatsAgain, this focuses on perimeter security rather than continuous, identity- and context-based access control.
From a Security+ perspective, Zero Trust is best represented by continuous validation before and during access, which makes C correct.

A content filter is a device or software that blocks or allows access to web content based on predefined rules or categories. In this case, the new retail website is mistakenly categorized as gambling by the content filter, which prevents users from accessing it. To resolve this issue, the content filter's categorization needs to be updated to reflect the correct category of the website, such as shopping or retail. This will allow the content filter to allow access to the website instead of blocking it.

A Host-based Intrusion Prevention System (HIPS) acts as a preventive control by actively blocking threats and a detective control by monitoring and alerting to suspicious activities on endpoints.
Reference:
CompTIA Security+ SY0-701 Official Study Guide, Domain 3.3: "HIPS combines preventive and detective capabilities to secure endpoints." Exam Objectives 3.3: "Summarize various security control types and methods."