单选题Chinese Wall模型的设计宗旨是（）。A 用户只能访问那些与已经拥有的信息不冲突的信息B 用户可以访问所有信息C 用户可以访问所有已经选择的信息D 用户不可以访问那些没有选择的信息

共用题干
Chinese Dialects（方言）

The enormous differences in Chinese dialects have been a continuing problem ever since China became an empire in 221 B.C.,and it is one big reason why the country has remained impoverished （贫穷）.Of the 600 million people,all but a very small number speak Chinese. But the dialects vary so widely that the speech of Peking,for example,is as different from the speech of Canton as English is from German.
There is,to be sure,only one written language for all China,but it bears no phonetic（语音的）relationship to any of the spoken dialects.Moreover,it has so many symbols that only a tiny portion of the population has ever mastered it.
As a result,most Chinese have been isolated for centuries from a free flow of ideas and from the economic progress that such a flow produces.Many dynasties tried with little success to break down the wall. After recognizing the importance of having a literate people for working in a technological world and for developing an effective propaganda（宣传）machine,the present government is putting everything it has into tackling the language problem. But the obstacles are so formidable（难以应付的）that the results cannot yet be predicted.
At the heart of the problem is the dialects.The dialects prevented the evolution of a single written language based on phonetics.Instead,the Chinese were forced to develop a system that has no relation to sound,and they have clung to it for more than 3,000 years.When this system is applied to a whole language,it results in an overwhelming number of symbols.
There are about 50,000 entries in a Chinese dictionary not counting the compounds（复合词）. In order to be literate,a Chinese must learn 6,000;to be moderately educated,12,000.An English-speaking child,having to conquer only a twenty-six-letter alphabet,has usually learned to read by the time he begins the third grade.A Chinese child needs at least five more years of elementary learning;in the seventh grade,he can barely read a Chinese newspaper.

The main reason why there are a great number of symbols in Chinese language is that______.
A:China failed to develop a single written language based on phonetics
B:a Chinese child is supposed to learn much more words than his English speaking counterpart
C:enormous differences in Chinese dialects
D:the Chinese language system has no relation to sound
E:educate more people to learn the same language
F: there is only a small part of the population who understand the large number of symbols