To answer this question, you need to understand the concepts of white box testing and black box testing.
White box testing, also known as structural testing or glass box testing, involves testing an application while having complete knowledge of its internal workings. This includes examining the source code, design documents, and implementation details. White box testing aims to test the internal logic of the application, such as control flow, data flow, and error handling.
Black box testing, on the other hand, involves testing an application without having any knowledge of its internal workings. Testers focus on the functional requirements of the application, and the testing is based on inputs and expected outputs. Black box testing aims to test the application from an end-user perspective, without considering the internal implementation.
In the given scenario, when you are performing EQA (External Quality Assurance) of an application developed by another project, you are doing black box testing. This is because you are testing the application without having knowledge of its internal workings, similar to how a typical end-user would interact with the application.
Therefore, the correct answer is B. black box testing.