The correct answer is D. Administrators create explicit rules in the rulebase. These are visible, administrator-defined policy rules that specify match conditions and actions. They can include source, destination, VPN, services/applications, content, action, track, install-on, and time conditions. Option A is wrong because implicit rules are automatically present as system behavior, such as layer cleanup behavior. Option B is wrong because implied rules are automatically generated from global properties or required Check Point control connections; the administrator can configure whether some implied rules apply, but they are not created as ordinary visible policy rules. Option C, “open,” is not a formal rule type in this context. The distinction matters during troubleshooting: if traffic is accepted or dropped before it reaches an explicit rule, implied rules or cleanup behavior may be involved. But the rules administrators directly author and maintain in SmartConsole are explicit rules. Reference topics: Explicit Rules, Implied Rules, Rule Base, Security Policy Management.