负责把不可靠的传输信道转换成可靠的传输信道,传送带有校验的数据帧,采用差错控制和帧顺

题型:单项选择题

问题:

负责把不可靠的传输信道转换成可靠的传输信道,传送带有校验的数据帧,采用差错控制和帧顺序控制功能的是哪一层?()

A.物理层

B.数据链路层

C.网络层

D.传输层

考点:华为认证考试华为认证数据通信工程师HCDA考试华为认证数据通信工程师HCDA考试题库
题型:单项选择题

在典型的市场营销环境中,客户所需要的物流服务会随时间而变化。为了能在动态条件下制定营销战略,企业常需要借助()来建模。

A.物流科学发展理论 

B.产品生命周期理论 

C.物流系统理论 

D.物流网络理论

题型:单项选择题

接地线要用截面积不小于30mm2的裸铜软绞线做成,并不得有断股、散股和接头。

题型:单项选择题

药品出库的原则有

A.后产先出

B.先产先出

C.先进先出

D.后进先出

E.一二类药先出

题型:单项选择题

马兜铃蜜炙后()

A.增强补中益气作用

B.缓和药性

C.增强润肺止咳作用

D.矫味、消除副作用

E.长于泻火解毒、化痰止咳

题型:单项选择题

Passage Two

When an invention is made, the inventor has three possible courses of action open to him: he can give the invention to the world by publishing it, keep the idea secret, or patent it.
A granted patent is the result of a bargain made between an inventor and the state, by which the inventor gets a limited period of monopoly (垄断) and publishes full details of his invention to the public after that period terminates (终止).
Only in most exceptional circumstances is the life-span of a patent extended to alter this normal process of events.
The longest extension ever granted was to Georges Valensi: his 1939 patent for color TV receiver circuitry was extended until 1971 because for most of the patent’s normal life there was no color TV to receive and thus no hope of reward for the invention.
Because a patent remains permanently public after it has terminated, the shelves of the library attached to the patent office contain details of literally millions of ideas that are free for anyone to use and, if older than half a century, sometimes even re-patent. Indeed, patent experts often advise anyone wishing to avoid the high cost of conducting a search through live patents that the one sure way of avoiding violation of any other inventor’s right is to plagiarize a dead patent. Likewise, because publication of an idea in any other form permanently invalidates (使无效) further patents on that idea, it is traditionally safe to take ideas from other areas of print. Much modern technological advance is based on these presumptions of legal security.
Anyone closely involved in patents and inventions soon learns that most "new" ideas are, in fact, as old as the hills. It is their reduction to commercial practice, either through necessity of dedication, or through the availability of new technology, that makes news and money. The basic patent for the theory magnetic recording dates back to 1886. Many of the original ideas behind television originate from the late 19th and early 20th century. Even the Volkswagen rear engine car was anticipated by a 1904 patent of a cart with the horse at the rear.

The word "plagiarize" (Line 5, Para. 5) most probably means ______ .

A.steal and use

B.give reward to

C.make public

D.take and change

更多题库