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问题 单项选择题 B型题

常温下脊髓能耐受完全缺血的时间是（）

A.3～5分钟

B.10～15分钟

C.20～40分钟

D.45分钟

E.60分钟

答案

参考答案：D

解析：4.高渗盐水刺激下丘脑-垂体分泌足量ADH，使尿量迅速减少。

选择题

向月球发射激光，经2.7s后接收到月球表面反射回来的激光，则月球和地球之间的距离为（激光在空间传播速度C=3×105km/s）[ ]

A、8.1×105km

B、4.05×105km

C、3×108km

D、3×105km
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单项选择题

The network layer provides services to the transport layer．It can be based on either (67) ．In both cases，its main job is (68) packets from the source to the destination．

In network layer，subnets can easily become congested，increasing the delay and (69) for packets．Network designers attempt to avoid congestion by proper design．Techniques include (70) policy,caching，flow control，and more．

The next step beyond just dealing with congestion is to actually try to achieve a promised quality of service．The methods that can be used for this include buffering at the client，trafficshaping，resource (71) ，and admission contr01．Approaches that have been designed forgood quality of service include integrated services(including RSVP)，differentiated services，andMPLS．

70（）

A．abandonment

B．retransmission

C．checksum

D．synchronism
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