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问题 选择题

下列变化中，属于物理变化的是（　　）

A．动物呼吸

B．光合作用

C．铜丝拉直

D．钢铁生锈

答案

A、动物呼吸能生成水和二氧化碳，属于化学变化．错误；

B、光合作用能生成葡萄糖和氧气，属于化学变化．错误；

C、铜丝拉直的过程中没有新物质生成，属于物理变化．正确；

D、钢铁生锈的过程中有新物质--铁锈生成，属于化学变化．错误．

故选C．

多项选择题

周期性健康检查（PHE）的优点是（）。

A.在具体时间、地点得知常见病及危险因素

B.对无症状人群进行早期发现，早期诊断，早期治疗

C.可进行有针对性检查

D.可节约卫生资源

E.可产生较高的经济和社会效益
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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．

68（）

A．sending

B．receiving

C．switching

D．routing
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