【单选题】

For nearly ten years, the Unified Modeling Language (UML) has been the industry standard for visualizing, specifying, constructing, and documenting the{{U}}(71){{/U}}of a software-intensive system.As the {{U}}(72){{/U}}standard modeling language, the UML facilitates communication and reduces confusion among project {{U}}(73){{/U}}. The recent standardization of UML 2.0 has further extended the language’s scope and viability. Its inherent expressiveness allows users to {{U}}(74) {{/U}}everything from enterprise information systems and distributed Web-based applications to real-time embedded systems. The UML is not limited to modeling software. In fact, it is expressive enough to model {{U}}(75){{/U}}systems, such as workflow in the legal system, the structure and behavior of a patient healthcare system, software engineering in aircraft combat systems, and the design of hardware. To understand the UML, you need to form a conceptual model of the language, and this requires learning three major elements: the UML’s basic building blocks, the rules that dictate how those building blocks may be put together, and some common mechanisms that apply throughout the UML.

A、classes
B．components
C．sequences
D．artifacts