Communications security is the discipline of preventing unauthorized interceptors from accessing telecommunications in an intelligible form, while still delivering content to the intended recipients. In the United States Department of Defense culture, it is often referred to by the abbreviation COMSEC. The field includes cryptosecurity, transmission security, emission security, traffic-flow security and physical security of COMSEC equipment.
All of the other answers are incorrect answers:
Information security Information security would be the overall program but communications security is the more specific and better answer. Information security means protecting information and information systems from unauthorized access, use, disclosure, disruption, modification, perusal, inspection, recording or destruction.
The terms information security, computer security and information assurance are frequently incorrectly used interchangeably. These fields are interrelated often and share the common goals of protecting the confidentiality, integrity and availability of information; however, there are some subtle differences between them.
These differences lie primarily in the approach to the subject, the methodologies used, and the areas of concentration. Information security is concerned with the confidentiality, integrity and availability of data regardless of the form the data may take: electronic, print, or other forms. Computer security can focus on ensuring the availability and correct operation of a computer system without concern for the information stored or processed by the computer.
Server security While server security plays a part in the overall information security program, communications security is a better answer when talking about data over the network and preventing interception. See publication 800-123 listed in the reference below to learn more.
Client security While client security plays a part in the overall information security program, communications security is a better answer. Securing the client would not prevent interception of data or capture of data over the network. Today people referred to this as endpoint security.
References:
http://csrc.nist.gov/publications/nistpubs/800-123/SP800-123.pdf and https://en.wikipedia.org/wiki/Information_security and https://en.wikipedia.org/wiki/Communications_security

Repeaters offer the simplest form of connectivity. They regenerate received electrical signals at their original strength between cable segments. Bridges are devices used to connect similar or dissimilar LANs together to form an extended LAN. Routers provide packet routing between network segments. Brouter are devices that combine router and bridge functionality. Source: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw-Hill/Osborne, 2002, chapter 7: Telecommunications and Network Security (page 397).

Section: Access Control
Explanation/Reference:
Bell-LaPadula Confidentiality Model10 The Bell-LaPadula model is perhaps the most well-known and significant security model, in addition to being one of the oldest models used in the creation of modern secure computing systems. Like the Trusted Computer System Evaluation Criteria (or TCSEC), it was inspired by early U.S. Department of Defense security policies and the need to prove that confidentiality could be maintained. In other words, its primary goal is to prevent disclosure as the model system moves from one state (one point in time) to another.
When the strong star property is not being used it means that both the property and the Simple Security Property rules would be applied.
The Star (*) property rule of the Bell-LaPadula model says that subjects cannot write down, this would compromise the confidentiality of the information if someone at the secret layer would write the object down to a confidential container for example.
The Simple Security Property rule states that the subject cannot read up which means that a subject at the secret layer would not be able to access objects at Top Secret for example.
You must remember: The model tells you about are NOT allowed to do. Anything else would be allowed. For example within the Bell LaPadula model you would be allowed to write up as it does not compromise the security of the information. In fact it would upgrade it to the point that you could lock yourself out of your own information if you have only a secret security clearance.
The following are incorrect answers because they are all FALSE:
"It allows read up" is incorrect. The "simple security" property forbids read up.
"It addresses covert channels" is incorrect. Covert channels are not addressed by the Bell-LaPadula model.
"It addresses management of access controls" is incorrect. Management of access controls are beyond the scope of the Bell-LaPadula model.
Reference(s) used for this question:
Hernandez CISSP, Steven (2012-12-21). Official (ISC)2 Guide to the CISSP CBK, Third Edition ((ISC)2 Press) (Kindle Locations 17595-17600). Auerbach Publications. Kindle Edition.

Explanation/Reference:
The primary objective of proper separation of duties is to ensure that one person acting alone cannot compromise the company's security in any way. A proper separation of duties does not prevent employees from disclosing information, nor does it ensure that access controls are in place or that audit trails are not tampered with.
Source: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw-Hill/Osborne, 2002, Chapter
12: Operations Security (Page 808).