单项选择题
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 suppors 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