Explanation/Reference:
Both are the components of a sensitivity label.
The following are incorrect:
A Classification Set and a single Compartment. Is incorrect because the nomenclature "Classification Set" is incorrect, there only one classifcation and it is not a "single compartment" but a Compartment Set.
A single classification and a single compartment. Is incorrect because while there only is one classifcation, it is not a "single compartment" but a Compartment Set.
A Classification Set and user credentials. Is incorrect because the nomenclature "Classification Set" is incorrect, there only one classifcation and it is not "user credential" but a Compartment Set. The user would have their own sensitivity label.

Section: Risk, Response and Recovery
Explanation/Reference:
Hierarchical Storage Management (HSM) provides a continuous on-line backup by using optical or tape
"jukeboxes," similar to WORMs.
Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, 2001, John Wiley & Sons, Page 71.

Volatile memory is Random Access Memory (RAM)

Explanation/Reference:
In order to protect against fraud in electronic fund transfers (EFT), the Message Authentication Code (MAC), ANSI X9.9, was developed. The MAC is a check value, which is derived from the contents of the message itself, that is sensitive to the bit changes in a message. It is similar to a Cyclic Redundancy Check (CRC).
The aim of message authentication in computer and communication systems is to verify that he message comes from its claimed originator and that it has not been altered in transmission. It is particularly needed for EFT Electronic Funds Transfer). The protection mechanism is generation of a Message Authentication Code (MAC), attached to the message, which can be recalculated by the receiver and will reveal any alteration in transit. One standard method is described in (ANSI, X9.9). Message authentication mechanisms an also be used to achieve non-repudiation of messages.
The Secure Electronic Transaction (SET) was developed by a consortium including MasterCard and VISA as a means of preventing fraud from occurring during electronic payment.
The Secure Hash Standard (SHS), NIST FIPS 180, available at http://www.itl.nist.gov/fipspubs/fip180-
1.htm, specifies the Secure Hash Algorithm (SHA-1).
Source:
KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, John Wiley & Sons, 2001, Chapter 4: Cryptography (page 170)
also see:
http://luizfirmino.blogspot.com/2011/04/message-authentication-code-mac.html and
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.22.2312&rep=rep1&type=pdf

Explanation/Reference:
Because the contingency plan contains potentially sensitive operational and personnel information, its distribution should be marked accordingly and controlled. Not all employees would obtain a copy, but only those involved in the execution of the plan.
All other statements are correct.
NOTE FROM CLEMENT:
I have received multiple emails stating the explanations contradict the correct answer. It seems many people have a hard time with negative question. In this case the Incorrect choice (the one that is not true) is the correct choice. Be very carefull of such questions, you will get some on the real exam as well.
Reference(s) used for this question:
SWANSON, Marianne, & al., National Institute of Standards and Technology (NIST), NIST Special Publication 800-34, Contingency Planning Guide for Information Technology Systems