To answer this question, you need to understand the concept of functional and non-functional testing methods.

Functional testing focuses on testing the functionality of a system or software application, ensuring that it performs the tasks it is intended to do. On the other hand, non-functional testing focuses on testing the quality attributes or characteristics of a system, such as performance, usability, reliability, security, etc.

Let's go through each option to understand why it is correct or incorrect:

Option A) System testing - System testing is a type of functional testing that verifies the behavior and functionality of the entire system as a whole. It tests whether the system meets the specified functional requirements. Therefore, it is a functional testing method.

Option B) Usability testing - Usability testing is a type of non-functional testing that focuses on evaluating the user-friendliness and ease of use of a system or software application. It assesses how easily users can learn, navigate, and use the system. Therefore, it is a non-functional testing method.

Option C) Performance testing - Performance testing is a type of non-functional testing that measures the performance and responsiveness of a system or software application under specific conditions. It assesses factors such as speed, scalability, reliability, and resource usage. Therefore, it is a non-functional testing method.

Option D) Both b and c - This option is correct because both usability testing and performance testing are non-functional testing methods.

Therefore, the correct answer is D) Both b and c. These options are non-functional testing methods because they focus on evaluating the quality attributes of a system rather than its functional behavior.

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