An application layer firewall can also be called a proxy.
"A presentation layer gateway" is incorrect. A gateway connects two unlike environments and is usually required to translate between diffferent types of applications or protocols.
This is not the function of a firewall.
"A session layer gateway" is incorrect. A gateway connects two unlike environments and is usually required to translate between diffferent types of applications or protocols. This is not the function of a firewall.
"A transport layer gateway" is incorrect. A gateway connects two unlike environments and is usually required to translate between diffferent types of applications or protocols. This is not the function of a firewall.
References:
CBK, p. 467
AIO3, pp. 486 - 490, 960

The use of a firewall is a requirement to protect a local area network (LAN) that has external connections without that you have no real protection from fraudsters.
The following answers are incorrect:
dial-up. This is incorrect because this offers little protection once the connection has been established.
passwords. This is incorrect because there are tools to crack passwords and once a user has been authenticated and connects to the external connections, passwords do not offer protection against incoming TCP packets.
fiber optics. This is incorrect because this offers no protection from the external connection.

Remember the term Public-Key Certificate is synonymous with Digital Certificate or Identity certificate.
The certificate itself provides the binding but it is the certificate authority who will go through the Certificate Practice Statements (CPS) actually validating the bindings and vouch for the identity of the owner of the key within the certificate.
As explained in Wikipedia:
In cryptography, a public key certificate (also known as a digital certificate or identity certificate) is an electronic document which uses a digital signature to bind together a public key with an identity
- information such as the name of a person or an organization, their address, and so forth. The certificate can be used to verify that a public key belongs to an individual.
In a typical public key infrastructure (PKI) scheme, the signature will be of a certificate authority (CA). In a web of trust scheme such as PGP or GPG, the signature is of either the user (a self-signed certificate) or other users ("endorsements") by getting people to sign each other keys. In either case, the signatures on a certificate are attestations by the certificate signer that the identity information and the public key belong together. RFC 2828 defines the certification authority (CA) as:
An entity that issues digital certificates (especially X.509 certificates) and vouches for the binding between the data items in a certificate.
An authority trusted by one or more users to create and assign certificates. Optionally, the certification authority may create the user's keys.
X509 Certificate users depend on the validity of information provided by a certificate. Thus, a CA should be someone that certificate users trust, and usually holds an official position created and granted power by a government, a corporation, or some other organization. A CA is responsible for managing the life cycle of certificates and, depending on the type of certificate and the CPS that applies, may be responsible for the life cycle of key pairs associated with the certificates
Source: SHIREY, Robert W., RFC2828: Internet Security Glossary, may 2000. and http://en.wikipedia.org/wiki/Public_key_certificate

"Need to Know and the Principle of Least Privilege are two standard axioms of high-security environments. A user must have a need-to-know to gain access to data or resources. Even if that ser has an equal or greater security classification than the requested information, if they do not have a need-to-know, they are denied access. A need-to-know is the requirement to have access to, knowledge about, or possession of data or a resource to perform specific work tasks. The principle of least privilege is the notion that users should be granted the least amount of access to the secure environment as possible for them to be able to complete their work tasks." Pg 399 Tittel: CISSP Study Guide

Section: Security and Risk Management