下列网络互连设备中，属于物理层的是 (66) ，属于网络层的是 (67) 。

（66）处填（）。

A．中继器

B．交换机

C．路由器

D．网桥

Object-oriented analysis (OOA) is a semiformal specification technique for the object-oriented paradigm. Object-oriented analysis consists of three steps. The first step is (71) . It determines how the various results are computed by the product and presents this information in the form of a (72) . and associated scenarios. The second is (73) , which determines the classes and their attributes; Then determine the interrelationships and interaction among the classes. The last step is (74) , which determines the actions performed by or to each class or subclass and presents this information in the form of (75) .

A. collaboration diagramB. sequence diagram
C. use-case diagram D. activity diagram