A security domain is a domain of trust that shares a single security policy and single management.
The term security domain just builds upon the definition of domain by adding the fact that resources within this logical structure (domain) are working under the same security policy and managed by the same group.
So, a network administrator may put all of the accounting personnel, computers, and network resources in Domain 1 and all of the management personnel, computers, and network resources in Domain 2. These items fall into these individual containers because they not only carry out similar types of business functions, but also, and more importantly, have the same type of trust level. It is this common trust level that allows entities to be managed by one single security policy.
The different domains are separated by logical boundaries, such as firewalls with ACLs, directory services making access decisions, and objects that have their own ACLs indicating which individuals and groups can carry out operations on them.
All of these security mechanisms are examples of components that enforce the security policy for each domain. Domains can be architected in a hierarchical manner that dictates the relationship between the different domains and the ways in which subjects within the different domains can communicate. Subjects can access resources in domains of equal or lower trust levels.
The following are incorrect answers: The reference monitor is an abstract machine which must mediate all access to subjects to objects, be protected from modification, be verifiable as correct, and is always invoked. Concept that defines a set of design requirements of a reference validation mechanism (security kernel), which enforces an access control policy over subjects' (processes, users) ability to perform operations (read, write, execute) on objects (files, resources) on a system. The reference monitor components must be small enough to test properly and be tamperproof. The security kernel is the hardware, firmware and software elements of a trusted computing base that implement the reference monitor concept.
The security perimeter includes the security kernel as well as other security-related system functions that are within the boundary of the trusted computing base. System elements that are outside of the security perimeter need not be trusted. not every process and resource falls within the TCB, so some of these components fall outside of an imaginary boundary referred to as the security perimeter. A security perimeter is a boundary that divides the trusted from the untrusted. For the system to stay in a secure and trusted state, precise communication standards must be developed to ensure that when a component within the TCB needs to communicate with a component outside the TCB, the communication cannot expose the system to unexpected security compromises. This type of communication is handled and controlled through interfaces.
Reference(s) used for this question:
Harris, Shon (2012-10-25). CISSP All-in-One Exam Guide, 6th Edition (Kindle Locations 28548-
28550). McGraw-Hill. Kindle Edition.
Harris, Shon (2012-10-25). CISSP All-in-One Exam Guide, 6th Edition (Kindle Locations 7873-
7877). McGraw-Hill. Kindle Edition.
Harris, Shon (2012-10-25). CISSP All-in-One Exam Guide, 6th Edition , Access Control, Page
214-217
Schneiter, Andrew (2013-04-15). Official (ISC)2 Guide to the CISSP CBK, Third Edition : Security
Architecture and Design (Kindle Locations 1280-1283). . Kindle Edition.
TIPTON, Hal, (ISC)2, Introduction to the CISSP Exam presentation.
AIO 6th edition chapter 3 access control page 214-217 defines Security domains. Reference
monitor, Security Kernel, and Security Parameter are defined in Chapter 4, Security Architecture
and Design.

Amutual aid agreement is used by two or more parties to provide
for assistance if one of the parties experiences an emergency. It is
expected that the other parties will assist the affected party in various
ways, perhaps by making office space available, or computing
time or resources, or supplying manpower if needed. While mutual
aid agreements may be a very cost-effective solution for disaster
recovery, it does not provide for full operations redundancy. An
example of a problem with a total reliance on mutual aid would be
the event that affects all parties to the agreement, thereby rendering
the agreement useless. While they are an effective means to provide
some resources to the organization in an emergency, they in themselves
are not a replacement for a full disaster recovery plan, including
alternate computer processing sites.
*Answer "A management-level analysis that identifies the impact of losing an entitys resources"
describes a business continuity plan.
*Answer "An appraisal or determination of the effects of a disaster on human, physical, economic,
and natural resources" describes a damage assessment
*answer "Activities taken to eliminate or reduce the degree of risk to life and property" describes
risk mitigation.
Source: NFPA 1600 Standard on Disaster/Emergency Management
and Business Continuity, National Fire Protection Association, 2000
edition, and Emergency Management Guide for Business and
Industry, Federal Emergency Management Agency, August 1998.

The main task here is the authentic distribution of the new root CA certificate as new trust anchor to all the PKI participants (e.g. the users).
In some of the rollover-scenarios there is no automatic way, often explicit assignment of trust from each user is needed, which could be very costly.
Other methods make use of the old root CA certificate for automatic trust establishment
(see PKIX-reference), but these solutions works only well for scenarios with currently valid root CA certificates (and not for emergency cases e.g. compromise of the current root CA certificate).
The rollover of the root CA certificate is a specific and delicate problem and therefore are often ignored during PKI deployment.
Reference: Camphausen, I.; Petersen, H.; Stark, C.: Konzepte zum Root CA
Zertifikatswechsel, conference Enterprise Security 2002, March 26-27, 2002, Paderborn;
RFC 2459 : Internet X.509 Public Key Infrastructure Certificate and CRL Profile.