单项选择题 “容器是一个构件，构件不一定是容器；一个容器可以包含一个或多个构件，一个构件只能 包含在一个容器中”。根据上述描述，如果用UML类图对容器和构件之间的关系进行面向对象分析和建模，则容器类和构件类之间存在（）关系。 ①继承②扩展③聚集④包含

单项选择题 Most of the host operating system provides a way for a system administrator to manually configure the IP information needed by a host .Automated configuration methods such as （）, are required to solve the problem.

单项选择题 OSI is a theoretical model that shows how any two different systems can communicate with each other. Router, as a networking device, operate at the （） layer of the OSI model.