Threat analysis is the examination of threat sources against system vulnerabilities to determine the threats for a particular system in a particular operational environment.
The following answers are incorrect:
Risk analysis is the process of identifying the risks to system security and determining the probability of occurrence, the resulting impact, and the additional safeguards that mitigate this impact.
Risk analysis is synonymous with risk assessment and part of risk management, which is the ongoing process of assessing the risk to mission/business as part of a risk-based approach used to determine adequate security for a system by analyzing the threats and vulnerabilities and selecting appropriate, cost-effective controls to achieve and maintain an acceptable level or risk.
Due Diligence is identifying possible risks that could affect a company based on best practices and standards.
Reference(s) used for this question:
STONEBURNER, Gary & al, National Institute of Standards and Technology (NIST), NIST Special Publication 800-27, Engineering Principles for Information Technology Security (A Baseline for Achieving Security), June 2001 (page B-3).

Even thou all 4 terms are very close to each other, the best choice is Excessive Privileges which would include the other three choices presented.
Reference(s) used for this question:
HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw-Hill/Osborne, 2001, Page 645. and

Explanation/Reference:
The (star) property of the Bell-LaPadula access control model states that writing of information by a subject at a higher level of sensitivity to an object at a lower level of sensitivity is not permitted (no write down).
Source: KRUTZ, Ronald L. & VINES, Russel D., The CISSP Prep Guide: Mastering the Ten Domains of Computer Security, John Wiley & Sons, 2001, Chapter 5: Security Architectures and Models (page 202).
Also check out: HARRIS, Shon, All-In-One CISSP Certification Exam Guide, McGraw-Hill/Osborne, 2002, Chapter 5: Security Models and Architecture (page 242, 243).

XSS or Cross-Site Scripting is a threat to web applications where malicious
code is placed on a website that attacks the use using their existing authenticated session status.
Cross-Site Scripting attacks are a type of injection problem, in which malicious scripts are
injected into the otherwise benign and trusted web sites. Cross-site scripting (XSS) attacks
occur when an attacker uses a web application to send malicious code, generally in the
form of a browser side script, to a different end user. Flaws that allow these attacks to
succeed are quite widespread and occur anywhere a web application uses input from a
user in the output it generates without validating or encoding it.
An attacker can use XSS to send a malicious script to an unsuspecting user. The end
user's browser has no way to know that the script should not be trusted, and will execute
the script. Because it thinks the script came from a trusted source, the malicious script can
access any cookies, session tokens, or other sensitive information retained by your
browser and used with that site. These scripts can even rewrite the content of the HTML page.
Mitigation:
Configure your IPS - Intrusion Prevention System to detect and suppress this traffic.
Input Validation on the web application to normalize inputted data.
Set web apps to bind session cookies to the IP Address of the legitimate user and only
permit that IP Address to use that cookie.
See the XSS (Cross Site Scripting) Prevention Cheat Sheet
See the Abridged XSS Prevention Cheat Sheet
See the DOM based XSS Prevention Cheat Sheet
See the OWASP Development Guide article on Phishing.
See the OWASP Development Guide article on Data Validation.
The following answers are incorrect:
Intrusion Detection Systems: Sorry. IDS Systems aren't usually the target of XSS attacks
but a properly-configured IDS/IPS can "detect and report on malicious string and suppress
the TCP connection in an attempt to mitigate the threat.
Firewalls: Sorry. Firewalls aren't usually the target of XSS attacks.
DNS Servers: Same as above, DNS Servers aren't usually targeted in XSS attacks but
they play a key role in the domain name resolution in the XSS attack process.
The following reference(s) was used to create this question: CCCure Holistic Security+ CBT and Curriculum and https://www.owasp.org/index.php/Cross-site_Scripting_%28XSS%29

Section: Cryptography
Explanation/Reference:
X.509 is used in digital certificates. X.400 is used in e-mail as a message handling protocol. X.25 is a standard for the network and data link levels of a communication network and X.75 is a standard defining ways of connecting two X.25 networks.
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 164).