What action should be taken to apply protection features if the Deep Security Agent is not active?

The action needed to apply protection features when the Deep Security Agent is not active is to activate the Virtual Appliance. The Virtual Appliance serves as a protective layer, managing security for the virtual machines in its environment. When the agent is not functioning or inactive, the Virtual Appliance can still ensure that security features such as anti-malware, intrusion prevention, and firewall capabilities are operational.

Activating the Virtual Appliance allows the security measures tied to it to be applied to the virtual machines, even in the absence of a fully operational Deep Security Agent. This setup is particularly useful in virtualized environments where maintaining constant agent availability can be challenging.

The other options, while related to protection features, do not directly address the situation of an inactive Deep Security Agent. Enabling Guest Introspection Service or using Appliance Only settings may not guarantee that security measures will be enforced in the same manner as activating the Virtual Appliance. Deploying the Agent is necessary for long-term protection but does not resolve the immediate issue of applying security features when the agent is inactive.