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问题 单项选择题

在计算机网络中，采用CRC进行差错校验，假设生成多项式为G(X)=X4+X+1，信息码字为11010，则计算出的CRC校验码以及接收端发现错误后采取的措施分别是______。

A．0000，重新生成原始数据
B．1000，自动请求重发
C．0110，自动请求重发
D．1001，重新生成原始数据

答案

参考答案：B

解析： 依题意，生成多项式G(X)=X4+X+1，其对应的二进制表示为10011，产生的校验码是4位。若信息码字为11010，则其CRC校验码计算过程如下：
可见，计算出的结果就是CRC校验码字“1000”。当接收端发现数据在传输过程中出错时，将采用自动请求重传(ARQ)方式来纠正错误。

单项选择题

It should go without saying that the focus of UML is modeling. However, what that means, exactly, can be an open-ended question. (71) is a means to capture ideas, relationships, decisions, and requirements in a well-defined notation that can be applied to many different domains. Modeling not only means different things to different people, but also it can use different pieces of UML depending on what you are trying to convey. In general, a UML model is made up of one or more (72) . A. diagram graphically represents things, and the relationships between these things. These (73) can be representations of real-world objects, pure software constructs, or a description of the behavior of some other objects. It is common for an individual thing to show up on multiple diagrams; each diagram represents a particular interest, or view, of the thing being modeleD. UML 2.0 divides diagrams into two categories: structural diagrams and behavioral diagrams. (74) are used to capture the physical organization of the things in your system, i.e., how one object relates to another. (75) focus on the behavior of elements in a system. For example, you can use behavioral diagrams to capture requirements, operations, and internal state changes for elements.

（74）处填（）。

A．Activity diagrams

B．Use-case diagrams

C．Structural diagrams

D．Behavioral diagrams
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单项选择题

煤炭验收动态轨道衡合理距离处设有明显（）标志。

A.限高

B.限速

C.限宽
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