Which example illustrates a non-functional requirement?

• A. Process orders.
• B. System uptime 99.9%.
• C. Implement login feature.
• D. Generate annual report.

Answer: (B)

Non-functional requirements specify how a system must be or operate, focusing on quality attributes and constraints like availability, performance, or security. A target like system uptime 99.9% is a reliability/availability constraint for the whole system—it's about how often the system is up and usable, and it’s measurable (often tracked in an SLA). It doesn’t describe a specific feature the system must perform; rather, it sets a standard for its operation over time.

The other options describe concrete features or functions the system should provide (processing orders, implementing a login feature, generating a report), which are functional requirements. So the uptime target best fits the category of a non-functional requirement.