To answer this question, we need to understand the difference between functional and nonfunctional requirements.
Functional requirements specify the behavior of a system or its components and describe what the system should do. They focus on the functionality or capabilities of the system.
Nonfunctional requirements, on the other hand, specify the qualities or characteristics of a system. These requirements describe how the system should perform, rather than what it should do.
Let's go through each option to determine which one is an example of a nonfunctional requirement:
A. Requirements - This option is not an example of a nonfunctional requirement. "Requirements" is a general term that can refer to both functional and nonfunctional requirements.
B. Defect density - This option is not an example of a nonfunctional requirement. Defect density is a measure used to evaluate the quality of a software product, but it does not specify a quality or characteristic of the system itself.
C. Failure Modes - This option is not an example of a nonfunctional requirement. Failure modes refer to the different ways in which a system can fail, but they do not specify a quality or characteristic of the system itself.
D. Availability - This option is an example of a nonfunctional requirement. Availability specifies the desired level of system uptime or the amount of time the system should be operational. It describes a quality or characteristic of the system.
E. Specifications - This option is not an example of a nonfunctional requirement. Specifications can refer to both functional and nonfunctional requirements, depending on the context.
Therefore, the correct answer is D) Availability. This option is an example of a nonfunctional requirement because it specifies the desired level of system uptime.