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问题 选择题

下列有关实验现象描述错误的是（　　）

A．氢气在空气中燃烧发出淡蓝色火焰

B．木炭在空气中燃烧后生成二氧化碳

C．硫在氧气中燃烧发出明亮的蓝紫色火焰

D．铁丝在氧气里剧烈燃烧，火星四射

答案

A、氢气在空气中燃烧，发出淡蓝色火焰，故选项说法正确．

B、木炭在空气中燃烧后生成二氧化碳，是实验结论而不是实验现象，故选项说法错误．

C、硫在氧气中燃烧，发出明亮的蓝紫色火焰，故选项说法正确．

D、铁丝在氧气中剧烈燃烧，火星四射，故选项说法正确．

故选B．

单项选择题

One of the most widely used routing protocols in IP networks is the Routing Information Protocol(RIP)．RIP is the canonical example of a routing protocol built on the (71) algorithm．Routing protocols in internetworks differ slightly from the idealized graph model．In aninternetwork，the goal of the routers to forward packets to various (72) ．

Routers running RIP send their advertisement about cost every (73) seconds．A router also sends an update message whenever an update from another router causes it to change itsrouting table．

It is possible to use a range of different metrics or costs for the links in a routing protocol．RIP takes the simplest approach，with all link costs being equal (74) Thus it always tries tofind the minimum hop route．Valid distances are 1 through (75) ．This also limits RIP torunning on fairly small networks．

（74）处应填（）。

A．1

B．15

C．16

D．length of the link
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单项选择题

一般高血压患者降压目标为（）

A.SBp<140/90mmHg

B.SBp≦140/90mmHg

C.SBp<160/90mmHg

D.SBp<160/95mmHg

E.SBp<120/80mmHg
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