In a world where it seems we already have too much to do, and too many things to think about, it seems the last thing we need is something new that we have to learn.    But use cases do solve a problem with requirements: with __1__ declarative requirements it's hard to describe steps and sequences of events.    Use cases, stated simply, allow description of sequences of events that, taken together, lead to a system doing something useful. As simple as this sounds, this is important. When confronted only with a pile of requirements, it's often __2__ to make sense of what the authors of the requirements really wanted the system to do. In the preceding example, use cases reduce the ambiguity of the requirements by specifying exactly when and under what conditions certain behavior occurs; as such, the sequence of the behaviors can be regarded as a requirement. Use cases are particularly well suited to capturing these kind of requirements. Although this may sound simple, the fact is that __3__ requirement capture approaches, with their emphasis on declarative requirements and "shall" statements, completely fail to capture the __4__ of the system's behavior. Use cases are a simple yet powerful way to express the behavior of the system in way that all stakeholders can easily understand.    But, like anything, use cases come with their own problems, and as useful as they are, they can be __5__. The result is something that is as bad, if not worse, than the original problem. Therein it's important to utilize use cases effectively without creating a greater problem than the one you started with.
2、_____

答案：

解析：