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问题 选择题

光通过各种不同的障碍物后会产生各种不同的衍射条纹，衍射条纹的图样与障碍物的形状相对应，这一现象说明

A．光是机械波，且可以携带信息

B．光具有波动性，且可以携带信息

C．光具有粒子性，但不可携带信息

D．光具有波粒二象性，但不可携带信息

答案

答案：B

题目分析：本题意说光通过各种不同的障碍物后会产生各种不同的衍射条纹说明光是一种波，而无法说明光是电磁波，只能说明光具有波动性而不能说明光具有粒子性．衍射条纹的图样与障碍物的形状相对应说明光可以携带信息．

A、光是电磁波，但本题题干只能说明光是一种波，而无法说明光是电磁波，故A错误．

B、既然光能够发生衍射现象，则光一定是一种波，既然是波，就具有波动性，故B正确．

C、光具有粒子性，衍射条纹的图样与障碍物的形状相对应，说明光可以携带信息，故C错误．

D、光具有波粒二象性，可携带信息，故D错误．

故选B．

点评：本题是一道不可多得的好题，告诉同学们解题或处理问题时一定要从因到果，而不能无中生有．

单项选择题 案例分析题

26岁，初产妇，40周妊娠，因规律宫缩6小时入院。胎心监护提示胎心基线160次／分，伴有早期减速，B超提示脐带绕颈1周。 * * 检查：胎头位置坐骨棘上1cm，宫口开大3cm，胎膜未破，估计胎儿体重3300～3500g，骨盆测量正常。

此时应立即采取何种措施不包括（）

A.左侧卧位

B.吸氧

C.臀高位

D.监测胎心

E.立即剖宫产
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单项选择题

Typically, these are concern with the establishment of (66) the network and with the control of the flow of messages across this channel. The provision of such facilities is only part of the network requirements, however, since in many applications the communicating computers may be of different types. This means that they may use different programming languages and, more importantly, different forms of (67) interface between user(application)program, normally referred to, as application processes or APs, and the underlying communication services may be (68) For example, one computer may be a small single -user computer, while another may be a large (69) system. In the earlier days of computer communication, these issues meantthat only closed communities of computers ( that is, from the same manufacturer) could communicate with each other in a meaningful way. IBM’s Systems Network.
Architecture (SNA) and DEC’s Digital Network Architecture (DNA) are just two examples of Communication software packages produced by manufacturers to allow their systems to be int erconnected together. These proprietary packages, however, of which there am still many inexistence, do not address the problem of universal interconnect ability, or open systems interconnection. In an attempt to alleviate this problem, (70) , in the late 1970s, formulated a reference model to provide a common basis ( or the coordination of standards developments and to allow existing and evolving standards activities to beplaced into perspective with one another.

A．communication channel access

B．protocols

C．data channel

D．public communication
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