Stress testing primarily evaluates the performance aspect of a software system. It aims to determine how the system handles heavy workloads and high stress conditions, including response times and resource utilization.

Control flow testing is the technique used to validate that loops and conditional statements in the code are working as expected. It examines the paths through the code to ensure that all logical conditions are adequately tested.

Integration testing is conducted before system testing to ensure that different modules work together as a coherent system. It focuses on verifying the interactions and data flow between modules, which is crucial before evaluating the system as a whole.

One of the goals of software reverse engineering is to identify potential bugs or defects within the system. By examining the source code or binary, reverse engineers can uncover vulnerabilities and issues that may need to be addressed to improve the software's reliability and security.

In this scenario, where the software needs to accommodate future changes due to evolving market demands, adaptive maintenance is crucial. Adaptive maintenance involves making changes to the software to ensure it remains functional and relevant in the face of changing requirements. This type of maintenance is essential to keep the software in sync with market needs.

In Test-Driven Development (TDD), unit tests are written before the code implementation. This approach ensures that each unit of code is thoroughly tested before it's even created, helping to identify and prevent defects early in the development process.

Regression testing is typically performed after code changes are made and before a new release or update of the software. It ensures that existing functionality remains intact after modifications.

Preventive maintenance focuses on anticipating and preventing issues before they occur. It involves tasks such as code reviews, proactive bug-fixing, and performance optimization to maintain the system's reliability.

A compliance audit is performed to ensure that all contractual agreements, legal requirements, and specified standards have been fulfilled. In the context of software engineering, this type of audit is crucial to confirm that the product adheres to all requirements and agreements.

The principle suggesting that derived classes must be substitutable for their base classes is "Polymorphism." It allows objects of derived classes to be used where objects of the base class are expected, enabling flexibility and extensibility in software design.

One of the major challenges in software maintenance, especially when dealing with old and obsolete technologies, is ensuring compatibility with modern hardware. As hardware and software evolve, older technologies may no longer be supported, leading to compatibility issues.

The main objective of regression testing is to ensure that new code changes do not introduce new defects or issues in the existing functionality of the software. It helps maintain the overall quality and reliability of the software.