One the most secure implementations of firewall architectures is the screened-subnet firewall. It employs two packet-filtering routers and a bastion host. Like a screened host firewall, this firewall supports both packet-filtering and proxy services. 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 93).

Section: Security Operation Adimnistration
Explanation/Reference:
This responsibility would be delegated to a data custodian rather than being performed directly by the information owner.
"Determine what level of classification the information requires" is incorrect. This is one of the major responsibilities of an information owner.
"Periodically review the classification assignments against business needs" is incorrect. This is one of the major responsibilities of an information owner.
"Delegates responsibility of maintenance of the data protection mechanisms to the data custodian" is incorrect.
This is a responsibility of the information owner.
References:
CBK p. 105.
AIO3, p. 53-54, 960

Firewall rules can be used to enable access for traffic to specific ports or services. "Service numbers" is rather stilted English but you may encounter these types of wordings on the actual exam -- don't let them confuse you.
"Only unauthorized application port or service numbers" is incorrect. Unauthorized ports/services would be blocked in a properly installed firewall rather than permitting access.
"Only authorized application port or ex-service numbers" is incorrect. "Ex-service" numbers is a nonsense term meant to distract you.
"Only authorized application port or service integers." While service numbers are in fact integers, the more usual (and therefore better) answer is either service or "service number."
References
CBK, p. 464 AIO3, pp. 482 - 484

Explanation/Reference:
MAC provides high security by regulating access based on the clearance of individual users and sensitivity labels for each object. Clearance levels and sensitivity levels cannot be modified by individual users -- for example, user Joe (SECRET clearance) cannot reclassify the "Presidential Doughnut Recipe" from
"SECRET" to "CONFIDENTIAL" so that his friend Jane (CONFIDENTIAL clearance) can read it. The administrator is ultimately responsible for configuring this protection in accordance with security policy and directives from the Data Owner.
DAC is incorrect. In DAC, the data owner is responsible for controlling access to the object.
Access control matrix is incorrect. The access control matrix is a way of thinking about the access control needed by a population of subjects to a population of objects. This access control can be applied using rules, ACL's, capability tables, etc.
TACACS is incorrect. TACACS is a tool for performing user authentication.
References:
CBK, p. 187, Domain 2: Access Control.
AIO3, Chapter 4, Access Control.