由∠1+∠2=90 °，∠3+∠4=90 °，∠1=∠3，得∠2=∠4，其理由是（    ）．

To a router, a flow is a (1) of packets that share the same Characterstics, such as traveling the same (2) ,using the same (3) ,having the same kind of security, and so on. A router that supports the handling of flow labels has a (4) table. The table has an entry for each active flow label; each entry defines the (5) required by the corresponding flow label.

5（）

A．quality

B．Traffic

C．services

D．route