Which of the following is true about functional requirements ?

Functional requirements define the specific behaviors, functions, and services that a system must provide to meet user needs. They answer the question of what the system should do, such as processing transactions or generating reports, without detailing how these functions are implemented. This makes Option A the correct choice because it accurately captures the essence of functional requirements as behavioral specifications.\nOption B is incorrect because specifying how a system should be built relates to design decisions or non-functional constraints, not functional behavior. Option C is wrong as it describes non-functional requirements like reliability or usability, which focus on quality attributes rather than system functions. Option D is also incorrect because performance criteria fall under non-functional requirements, whereas functional requirements focus on the actual capabilities and actions the system must perform for its users.