某公司防火墙系统由包过滤路由器和应用网关组成。下列描述中，错误的是(7)。

(71)

(70)

(69)

(68)

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 determines 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) .

对于二叉查找树(Binary Search Tree)，若其左子树非空，则左子树上所有结点的值均小于根结点的值；若其右子树非空，则右子树上所有结点的值均大于根结点的值；左、右子树本身就是两棵二叉查找树。因此，对任意一棵二叉查找树进行(63)遍历可以得到一个结点元素的递增序列。在具有n个结点的二叉查找树上进行查找运算，最坏情况下的算法复杂度为(64)。

(66)

设一个包含N个顶点、E条边的简单有向图采用邻接矩阵存储结构(矩阵元素A[i][j]等于1/0分别表示顶点i与顶点j之间有/无弧)，则该矩阵的元素数目为(58)，其中非零元素数目为(59)。

(64)

某单位网络拓扑如图6-11所示，路由器R1～R7均运行OSPF协议。其中，(70)为主干路由器。