Identification is used to establish user accountability. Many times identification takes the form of a logon ID.

X.400 is used in e-mail as a message handling protocol. X.500 is used in directory services. X.509 is used in digital certificates and X.800 is used a network security standard.
Reference: http://www.alvestrand.no/x400/.

Explanation/Reference:
According to the authors, hackers fall in these categories, in increasing threat order: security experts, students, underemployed adults, criminal hackers, corporate spies and disgruntled employees.
Disgruntled employees are the most dangerous security problem of all because they are most likely to have a good knowledge of the organization's IT systems and security measures.
Source: STREBE, Matthew and PERKINS, Charles, Firewalls 24seven, Sybex 2000, Chapter 2: Hackers.

Explanation/Reference:
The ss (simple security) property of the Bell-LaPadula access control model states that reading of information by a subject at a lower sensitivity level from an object at a higher sensitivity level is not permitted (no read up).
Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, John Wiley & Sons, 2001, Chapter 5: Security Architectures and Models (page 202).

Section: Security Operation Adimnistration
Explanation/Reference:
First you have to realize that the question is specifically talking about a CDROM. The information stored on a CDROM is not in electro magnetic format, so a degausser woud be inneffective.
You cannot sanitize a CDROM but you might be able to sanitize a RW/CDROM. A CDROM is a write once device and cannot be overwritten like a hard disk or other magnetic device.
Physical Damage would not be enough as information could still be extracted in a lab from the undamaged portion of the media or even from the pieces after the physical damage has been done.
Physical Destruction using a shredder, your microwave oven, melting it, would be very effective and the best choice for a non magnetic media such as a CDROM.
Source: TIPTON, Hal, (ISC)2, Introduction to the CISSP Exam presentation.