Which of the following types of testing is primarily focused on validating the functionality of a system without considering the internal structure of the application? 

Black Box Testing is a software testing method where the tester focuses on verifying the application’s functionality against the specified requirements without examining the internal code structure or logic. This method tests the system's input-output behavior, ensuring that, given certain inputs, the expected outputs are produced. Black Box Testing is beneficial for assessing user experience, functionality, and usability, making it especially suitable for higher-level testing, such as System Testing and User Acceptance Testing (UAT). It allows testers to identify discrepancies between actual and expected outcomes, validating whether the system operates as intended from an end-user perspective, regardless of how the internal processes achieve these outcomes. Option A (White Box Testing) - White Box Testing requires knowledge of the internal structure and involves testing the logic and code paths directly, unlike Black Box Testing. Option B (Unit Testing) - Unit Testing, though it focuses on individual components, typically involves examining code and logic internally, aligning more with White Box Testing practices. Option D (Integration Testing) - Integration Testing checks the interaction between components or systems and may involve both internal and external perspectives, but it is not limited solely to the input-output relationship. Option E (Regression Testing) - Regression Testing ensures new code changes do not adversely affect existing functionality, often involving various types of testing, including both Black Box and White Box approaches.