It describes how test cases are derived from a use case. A use case is a description of a set of sequences of actions, including variants, that a system performs to yield an observable result of value to an actor1. An actor can be a human user or another system. Test cases are designed to cover various user behaviors, including basic, exceptional or alternative and error behaviors associated with each use case1. Option A is incorrect, as test cases derived from a use case are not based on non-functional requirements such as usability, but on functional requirements that describe what the system does1. Option C is incorrect, as test cases derived from a use case are not created using white-box test techniques, but using black-box test techniques that focus on the inputs and outputs of the system1. Option D is incorrect, as test cases derived from a use case are not based on pair testing, which is a technique that involves two testers working together to find defects1. References: 1, Section 4.2.4