Explanation/Reference:
Explanation:
VPN key (to not be confused with pre-shared key that is used for authentication).

VPN trust entities, such as a Check Point Internal Certificate Authority (ICA). The ICA is part of the

Check Point suite used for creating SIC trusted connection between Security Gateways, authenticating administrators and third party servers. The ICA provides certificates for internal Security Gateways and remote access clients which negotiate the VPN link.
VPN Domain - A group of computers and networks connected to a VPN tunnel by one VPN gateway

that handles encryption and protects the VPN Domain members.
VPN Community - A named collection of VPN domains, each protected by a VPN gateway.

Reference:
http://sc1.checkpoint.com/documents/R77/CP_R77_VPN_AdminGuide/13868.htm

D is the best answer given the choices.
Unified Policy
In R80 the Access Control policy unifies the policies of these pre-R80 Software Blades:

Explanation/Reference:

Policy Layers and Sub-Policies
R80 introduces the concept of layers and sub-policies, allowing you to segment your policy according to your network segments or business units/functions. In addition, you can also assign granular privileges by layer or sub-policy to distribute workload and tasks to the most qualified administrators
* With layers, the rule base is organized into a set of security rules. These set of rules or layers, are inspected in the order in which they are defined, allowing control over the rule base flow and the security functionalities that take precedence. If an "accept" action is performed across a layer, the inspection will continue to the next layer. For example, a compliance layer can be created to overlay across a cross- section of rules.
* Sub-policies are sets of rules that are created for a specific network segment, branch office or business unit, so if a rule is matched, inspection will continue through this subset of rules before it moves on to the next rule.
* Sub-policies and layers can be managed by specific administrators, according to their permissions profiles. This facilitates task delegation and workload distribution.
Reference: https://community.checkpoint.com/docs/DOC-1065