System Integrity means that all components of the system cannot be tampered with by unauthorized personnel and can be verified that they work properly.
The following answers are incorrect:
The software of the system has been implemented as designed. Is incorrect because this would fall under Trusted system distribution.
Users can't tamper with processes they do not own. Is incorrect because this would fall under Configuration Management.
Design specifications have been verified against the formal top-level specification. Is incorrect because this would fall under Specification and verification.
References:
AIOv3 Security Models and Architecture (pages 302 - 306)
DOD TCSEC - http://www.cerberussystems.com/INFOSEC/stds/d520028.htm

The best way to properly verify an application or system during a stress test would be to expose it to "live" data that has been sanitized to avoid exposing any sensitive information or Personally Identifiable Data (PII) while in a testing environment. Fabricated test data may not be as varied, complex or computationally demanding as "live" data. A production environment should never be used to test a product, as a production environment is one where the application or system is being put to commercial or operational use. It is a best practice to perform testing in a non-production environment.
Stress testing is carried out to ensure a system can cope with production workloads, but as it may be tested to destruction, a test environment should always be used to avoid damaging the production environment. Hence, testing should never take place in a production environment. If only test data is used, there is no certainty that the system was adequately stress tested.

The correct answer is "It uses an ESP for authentication and encryptio". The Encapsulating
Security Payload, (ESP) is a component of IPSec. Socket Security (SOCKS) is a transport layer, secure networking proxy protocol. SOCKS replaces the standard network systems calls with its own calls. These calls open connections to a SOCKS proxy server for client authentication, transparently to the user.
Common network utilities, like TELNET or FTP, need to be SOCKSified,
or have their network calls altered to recognize SOCKS proxy calls.
Source: Designing Network Security by Merike Kaeo (Cisco Press, 1999).

Reference: HARRIS, Shon, CISSP All In One Exam Guide. Chapter 4, pages 126-127. A very excellent discussion on this topic stating the steps and explaining the processess of those steps is paraphrased (hopefully coherently) here:
A user can identify themselves with a userid or account number.
To be authenticated, a user usually provides a second piece of the credential set, like a password, passphase, cryptographic key, anatomical attribute, a token or a Personal Identification Number, or PIN.
Once the user provides credentials and is properly identified, the system needs to determine it the user has the necessary rights and privileges to do so.
If the user DOES have those rights and privileges, he is authorized access.