Explanation/Reference:
An e-mail message's confidentiality is protected when encrypted with the receiver's public key, because he is the only one able to decrypt the message. The sender is not supposed to have the receiver's private key. By encrypting a message with its private key, anybody possessing the corresponding public key would be able to read the message. By encrypting the message with its public key, not even the receiver would be able to read the message.
Source: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw-Hill/Osborne, 2002, chapter
8: Cryptography (page 517).

The CIA triad stands for Confidentiality, Integrity and Availability.

Section: Access Control
Explanation/Reference:
Availability assures that a system's authorized users have timely and uninterrupted access to the information in the system. The additional access control objectives are reliability and utility. These and other related objectives flow from the organizational security policy. This policy is a high-level statement of management intent regarding the control of access to information and the personnel who are authorized to receive that information. Three things that must be considered for the planning and implementation of access control mechanisms are the threats to the system, the system's vulnerability to these threats, and the risk that the threat may materialize Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, 2001, John Wiley & Sons, Page 32.

Section: Network and Telecommunications
Explanation/Reference:
Asynchronous Communication is the basic language of modems and dial-up remote access systems.
Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, 2001, John Wiley & Sons, Page 100.

Section: Risk, Response and Recovery
Explanation/Reference:
Although a loss of skilled workers knowledge would cause the company a great loss, it is not identified as a specific loss criteria. It would fall under one of the three other criteria listed as distracters.
Source: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw-Hill/Osborne, 2002, chapter 9:
Disaster Recovery and Business continuity (page 598).