Section: Access Control
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: Cryptography
Explanation/Reference:
A Public Key Infrastructure (PKI) provides confidentiality, access control, integrity, authentication and non- repudiation.
It does not provide reliability services.
Reference(s) used for this question:
TIPTON, Hal, (ISC)2, Introduction to the CISSP Exam presentation.

In a full mesh topology, all network nodes are individually connected with
each other, providing the highest availability. A partial mesh topology can sometimes be
used to offer some redundancy.
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 106).

When using link encryption, packets have to be decrypted at each hop and encrypted again.
Information staying encrypted from one end of its journey to the other is a characteristic of end-to-end encryption, not link encryption. Link Encryption vs. End-to-End Encryption
Link encryption encrypts the entire packet, including headers and trailers, and has to be decrypted at each hop.
End-to-end encryption does not encrypt the IP Protocol headers, and therefore does not need to be decrypted at each hop.
Reference: All in one, Page 735 & Glossary
and
Source: WALLHOFF, John, CBK#5 Cryptography (CISSP Study Guide), April 2002 (page 6).

Explanation/Reference:
As script kiddies are low to moderately skilled hackers using available scripts and tools to easily launch attacks against victims.
The other answers are incorrect because :
Black hats is incorrect as they are malicious , skilled hackers.
White hats is incorrect as they are security professionals.
Phreakers is incorrect as they are telephone/PBX (private branch exchange) hackers.
Reference : Shon Harris AIO v3 , Chapter 12: Operations security , Page : 830