To illustrate the interaction of runtime building blocks, the techniques most suitable are Activity diagrams, Sequence diagrams, State diagrams, and Flowcharts. Activity diagrams depict the workflow from one activity to another, providing a clear visualization of sequence and conditions for coordination. Sequence diagrams detail how objects operate with one another and in what sequence, making them ideal for dynamic behavior. State diagrams describe the state changes of system entities, showing interactions as transitions between states. Flowcharts are effective in visualizing the sequence of steps and their interactions in the process. Other options such as Class diagrams focus on static structure, and depictions of screen flows, tabular descriptions, and numbered lists do not provide sufficient detail to illustrate interactions dynamically.

Flexibility refers to the ability of a system to adapt to changing requirements or conditions. When a system is highly flexible, it often results in increased complexity, which can make it harder to test. Therefore, flexibility reduces testability. Simplicity in design makes it easier to understand and maintain the system. A simpler system is more comprehensible because there are fewer components and interactions to consider.

The software architect is primarily responsible for the technical quality of the software implementation and ensuring that the software design is suitable for its intended purpose. The technical quality includes aspects such as maintainability, scalability, and adherence to architectural standards. Ensuring that the software design is suitable for its purpose ensures that the system fulfills the necessary requirements effectively. The performance of the software and ensuring it is free of errors are more specific concerns that can be handled by specialized roles like performance engineers and testers, respectively.