Explanation/Reference:
In a known plaintext attack, the attacker has the plaintext and ciphertext of one or more messages. The goal is to discover the key used to encrypt the messages so that other messages can be deciphered and read.
Source: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw-Hill/Osborne, 3rd Ed., chapter 8: Cryptography (page 676). Also check out: Handbook of Applied Cryptography 4th Edition by Alfred J. Menezes, Paul C. van Oorschot and Scott A. Vanstone.

It is the systems auditor that should lead the effort to ensure that the security controls are in place and effective. The audit would verify that the controls comply with polices, procedures, laws, and regulations where applicable. The findings would provide these to senior management.
The following answers are incorrect: the local security specialist. Is incorrect because an independent review should take place by a third party. The security specialist might offer mitigation strategies but it is the auditor that would ensure the effectiveness of the controls
the business manager. Is incorrect because the business manager would be responsible that the controls are in place, but it is the auditor that would ensure the effectiveness of the controls.
the central security manager. Is incorrect because the central security manager would be responsible for implementing the controls, but it is the auditor that is responsibe for ensuring their effectiveness.

Explanation/Reference:
From the published (ISC)2 goals for the Certified Information Systems Security Professional candidate:
The CISSP candidate should be familiar to communications and network security as it relates to voice, data, multimedia, and facsimile transmissions in terms of local area, wide area, and remote access.
Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, 2001, John Wiley & Sons, Page 57.

A major objective with Configuration Management is stability. The changes to the system are controlled so that they don't lead to weaknesses or faults in th system.
The following answers are incorrect:
system maintenance. Is incorrect because it is not the best answer. Configuration Management does control the changes to the system but it is not as important as the overall stability of the system.
system operations. Is incorrect because it is not the best answer, the overall stability of the system is much more important.
system tracking. Is incorrect because while tracking changes is important, it is not the best answer. The overall stability of the system is much more important.

Section: Risk, Response and Recovery
Explanation
Explanation/Reference:
The keyword is ' MOST CRITICAL ' and the correct answer is ' Management Support ' as the management must be convinced of its necessity and that's why a business case must be made. The decision of how a company should recover from any disaster is purely a business decision and should be treated as so.
The other answers are incorrect because :
Security policy is incorrect as it is not the MOST CRITICAL piece.
Availability of backup information processing facilities is incorrect as this comes once the organization has BCP Plans in place and for a BCP Plan , management support must be there.
Staff training comes after the plans are in place with the support from management.
Reference : Shon Harris , AIO v3 , Chapter-9: Business Continuity Planning , Page : 697.