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问题 单项选择题 A1型题

物质代谢的各条途径不是孤立和分隔的，而是互相联系的。在代谢网络中，哪一条循环途径在整个代谢途径中处于中心的位置（）

A.鸟氨酸循环

B.三羧酸循环

C.乳酸循环

D.枸橼酸-丙酮酸循环

E.磷酸戊糖途径

答案

参考答案：B

单项选择题

The network layer provides services to the transport layer．It can be based on either (71) ．In both cases，its main job is (72) packets from the source to the destination．

In network layer，subnets can easily become congested，increasing the delay and (73) .

for packets．Network designers attempt to avoid congestion by proper design．Techniques include (74) policy，caching，flowcontrol，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，traffic shaping，resource (75) ，and admission control．Approaches that have been designed for good quality of service include integrated services(including RSVP) ，differentiated services， and MPLS．

（71）处填（）。

A．virtual circuits or datagrams

B．TCP or UDP

C．TCP or IP

D．IP or ARP
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单项选择题

在地震区，桩基承载力极限状态的计算采用（）。

A.荷载效应的基本组合

B.荷载效应的标准组合

C.地震作用效应与荷载效应标准组合

D.地震作用与其他荷载效应的基本组合
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