Which of the following is an example of a non-functional requirement?

The selection identifies an example of a non-functional requirement accurately. Non-functional requirements specify criteria that can be used to judge the operation of a system, rather than specific behaviors or functions. In this case, stating that "the system shall process transactions within two seconds" outlines a performance requirement, which is a key aspect of non-functional requirements. This sets a standard for efficiency that the system must meet, emphasizing performance rather than a specific capability or feature of the system itself.

The other choices reflect functional requirements, as they detail specific functionalities or features that the system should provide. For instance, allowing users to create accounts is a clear feature of the system, while providing customer support options pertains to services that users can access. Additionally, generating sales reports monthly also describes a particular function that the system needs to perform. Each of these examples focuses on 'what' the system will do rather than 'how well' it should perform those tasks, aligning them with the category of functional requirements.