In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.

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.

1（）

A．sequence

B．stream

C．Queues

D．flow

关于牙齿正位器不正确的描述是（）.

A.用软橡胶或弹性塑料制作

B.装置于上下颌所有牙齿的冠部

C.有利于咬合关系及牙位的保持，效果良好

D.每天晚上戴用，白天也至少戴4小时

E.对于排列不整齐或扭转的切牙及深覆的患者保持效果最好