Which of the following is a type of functional testing?

Functional testing focuses on verifying that the software functions as intended according to the specified requirements. It evaluates the behavior of the application by testing its functionalities without considering the internal structure or workings.

Black box testing is a type of functional testing where the tester does not have access to the internal code or logic of the application. Instead, they focus on inputting data and examining the outputs to ensure that the software behaves as expected. This method is effective for validating features, user interactions, and overall usability from an end-user perspective.

In contrast, reliability testing generally assesses how dependable a system is during intended use over time, which is more about the software's quality attributes rather than specific functionalities. Regression testing aims to verify that recent code changes have not adversely affected existing features; while it can include functional tests, its primary purpose is to validate the stability of the application after modifications. Structural testing, on the other hand, is focused on the internal structures or workings of an application, often involving white-box testing techniques.

Choosing black box testing as a type of functional testing is accurate because it aligns directly with the definition and purpose of functional testing, emphasizing the inputs and outputs rather than the implementation details.