在TCP/IP参考模型中，应用层是最高的一层，它包括了所有的高层协议。下列协议中不属于应用层协议的是______。
A．HTTP
B．FIP
C．UDP
D．SMTP
参考答案：C
解析：[知识点] Internet通信协议——TCP/IP
[评析] 在TCP/IP中，UDP协议提供了简单的、不可靠的无连接服务，它不属于TCP/IP的最高层(应用层)，而是属于第二层，即传输层。
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| These days, it is easier for us to travel to other countries than ever before. However, there is a big difficulty that most of us 1 when we meet people in other countries, we cannot communicate with them. There are 2 where English is still not spoken, though it is the most widely known language. So, wouldn't it be _ 3_ if there was one language that could be understood by anyone anywhere in the world? Esperanto that was created in 1887 may be the world's 4 truly international language. In fact, although 5 artificial (人造的) languages have been already created, only Esperanto has had much success. Its learners say that it is about four times 6 to learn than other languages. Spelling and pronunciation are both easy, too. For example, it does not have silent 7 like the "h" in" honest". If you 8 a word, you can spell it without any difficulty. The grammar is also as simple as possible: only sixteen basic 9 , no irregular verbs (不规则动词), only six verb endings. In short, Esperanto should be attractive (有吸引力的) as a language to learn, 10 there is a problem: how many people have met anyone who can really speak it? Anyway, we hope that some day one language can be mastered easily by anyone.
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