Which of the following represents a functional requirement?

A functional requirement specifies what a system should do, focusing on the behaviors, functions, and capabilities that the system must deliver to users. The statement that the system must allow users to amend customer details clearly outlines a specific functionality that the system needs to provide. It emphasizes an action that users can perform, which directly relates to the core operations of the system regarding customer information management.

In contrast, the other options cover different aspects. For example, stating that the system must be password protected pertains to a security requirement rather than a functional one; it ensures only authorized users can access the system but does not describe a specific function or behavior of the system. Similarly, compliance with the Data Protection Act is focused on legal and regulatory standards, while the requirement of outputting reports within five minutes relates to performance criteria rather than defining what specific actions the system must support. Thus, option A stands out as the best example of a functional requirement since it describes a particular functionality of the system.