In agile projects, the high risk of regression is primarily due to the code churn that occurs as business needs change over the course of several sprints. This is inherent in the agile process, where requirements and solutions evolve through collaborative effort. The iterative nature of agile projects means that as new features are added or existing features are modified to meet evolving business needs, previously tested and stable parts of the software might be affected, leading to potential regression issues. This phenomenon is well-recognized in agile methodologies and necessitates rigorous regression testing practices to ensure that new changes do not adversely affect existing functionalities.

The whole-team approach in agile methodologies is beneficial because it leverages the diverse skill sets within the team for the project's benefit. In this collaborative environment, team members, including developers, testers, and business analysts, work closely together from the project's outset. This close collaboration ensures a better understanding of the project goals, more innovative solutions to problems, and a higher quality product. The whole-team approach encourages knowledge sharing and collective problem-solving, leading to more efficient and effective project outcomes. This approach contrasts with traditional methodologies, where roles are more siloed, and collaboration between different roles occurs less frequently.

A testable acceptance criterion must be specific, measurable, and verifiable, which makes option C the correct choice. Stating that 'the response time to confirm a customer submission must not exceed 5 seconds' provides a clear, quantifiable measure that can be tested to determine whether the criterion has been met. This contrasts with more subjective criteria, such as the system being 'easy to use,' which cannot be easily quantified or measured in a straightforward manner. The specificity of the response time allows for the creation of test cases that can confirm whether the system meets this particular requirement, thus making it a testable acceptance criterion.

The defect titled 'Payment for parking ticket is restricted to cash only (no credit card supported)' is out of scope for the given test charter titled 'Buy a bus ticket' because it pertains to a different functionality not covered by the charter. The charter focuses on the process of purchasing a bus ticket, which involves functionality such as selecting a ticket type, choosing a journey, and completing the transaction. A defect related to payment methods for a parking ticket does not relate to these functions and is therefore considered out of scope for the testing session focused on buying a bus ticket.

In an agile project, testers often perform tasks beyond traditional testing roles, including implementing test strategy (i), measuring and reporting test coverage (iii), and coaching the development team on relevant aspects of testing (iv). Implementing test strategy involves planning how testing will be conducted within the agile framework, ensuring that testing aligns with agile principles and practices. Measuring and reporting test coverage help the team understand the extent to which the codebase is tested, which is crucial for maintaining quality in fast-paced agile environments. Coaching the development team involves sharing knowledge on testing best practices and fostering a quality-centric mindset across the team. These activities contribute to the collaborative and iterative nature of agile projects, where continuous feedback and improvement are emphasized.