It's because the question is at what point should the "functionality" has been "established correctly" - it is during the system design that when "defining the architecture, modules, interfaces, and data for a system is identified or established to satisfy specified requirement"

This answer surprised me. Appreciate comment that would justify correct answer.

Similar for me. I would like comments to justify the answer

B. During testing of the new application. An internal auditor should verify that the new application's connectivity to the organization's other systems has been established correctly during the testing phase of the systems development process. This is an important step to ensure that the new application functions as intended and properly integrates with the existing systems within the organization. By conducting this verification during testing, any connectivity issues or integration problems can be identified and addressed before the application is fully implemented and put into production.

I think it is because the New application has to be implemented first and, then, we test its connectivity and, then, we test the application + connectivity. Maintenance is totally a subsequent thing. Difficult and risky to check the connectivity before the application is implemented.