Explanation/Reference:
Making the determination to decide what level of classification the information requires is the main responsibility of the data owner.
The data owner within classification is a person from Management who has been entrusted with a data set that belong to the company. It could be for example the Chief Financial Officer (CFO) who has been entrusted with all financial date or it could be the Human Resource Director who has been entrusted with all Human Resource data. The information owner will decide what classification will be applied to the data based on Confidentiality, Integrity, Availability, Criticality, and Sensitivity of the data.
The Custodian is the technical person who will implement the proper classification on objects in accordance with the Data Owner. The custodian DOES NOT decide what classification to apply, it is the Data Owner who will dictate to the Custodian what is the classification to apply.
NOTE:
The term Data Owner is also used within Discretionary Access Control (DAC). Within DAC it means the person who has created an object. For example, if I create a file on my system then I am the owner of the file and I can decide who else could get access to the file. It is left to my discretion. Within DAC access is granted based solely on the Identity of the subject, this is why sometimes DAC is referred to as Identity Based Access Control.
The other choices were not the best answer
Running regular backups is the responsibility of custodian.
Audit the data users is the responsibility of the auditors
Periodically check the validity and accuracy of the data is not one of the data owner responsibility Reference(s) used for this question:
KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, John Wiley & Sons, 2001, Page 14, Chapter 1: Security Management Practices.

Displaying the directory contents of a folder can alter the last access time on each listed file.
Using a write blocker is wrong because using a write blocker ensure that you cannot modify the data on the host and it prevent the host from writing to its hard drives.
Made a full-disk image is wrong because making a full-disk image can preserve all data on a hard disk, including deleted files and file fragments.
Created a message digest for log files is wrong because creating a message digest for log files. A message digest is a cryptographic checksum that can demonstrate that the integrity of a file has not been compromised (e.g. changes to the content of a log file)
Domain: LEGAL, REGULATIONS, COMPLIANCE AND INVESTIGATIONS
References: AIO 3rd Edition, page 783-784 NIST 800-61 Computer Security Incident Handling guide page 3-18 to 3-20

Explanation/Reference:
UDP is a scaled-down version of TCP. It is used like TCP, but only offers a "best effort" delivery. It is connectionless, does not offer error correction, does not sequence the packet segments, and less reliable than TCP but because of its lower overhead, it provides a faster transmission than TCP.
Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, John Wiley & Sons, 2001, Chapter 3: Telecommunications and Network Security (page
86).

Section: Access Control
Explanation/Reference:
The principle of least privilege refers to allowing users to have only the access they need and not anything more. Thus, certain users may have no need to access any of the files on specific systems.
The following answers are incorrect:
Users can access all systems. Although the principle of least privilege limits what access and systems users have authorization to, not all users would have a need to know to access all of the systems. The best answer is still Users would get access to only the info for which they have a need to know as some of the users may not have a need to access a system.
Users get new privileges when they change positions. Although true that a user may indeed require new privileges, this is not a given fact and in actuality a user may require less privileges for a new position. The principle of least privilege would require that the rights required for the position be closely evaluated and where possible rights revoked.
Authorization creep. Authorization creep occurs when users are given additional rights with new positions and responsibilities. The principle of least privilege should actually prevent authorization creep.
The following reference(s) were/was used to create this question:
ISC2 OIG 2007 p.101,123
Shon Harris AIO v3 p148, 902-903

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.