问题 单项选择题

在FTP协议中,控制连接是由()主动建立的。

A.服务器端

B.客户端

C.操作系统

D.服务提供商

答案

参考答案:B

解析:

[分析]:

文件传输协议FTP利用TCP连接在客户机和服务器之间上传和下载文件。FTP协议占用了两个TCP端口,FTP服务器监听21号端口,准备接受用户的连接请求。当用户访问FTP服务器时便主动与服务器的21号端口建立控制连接。如果用户要求下载文件,则必须等待服务器的20号端口主动发出建立数据连接的请求,文件传输完成后数据连接随之释放。在客户端看来,这种处理方式被叫做被动式FTP,Windows系统中默认的就是这种处理方式。由于有的防火墙阻止由外向内地主动发起的连接请求,所以FTP数据连接可能由于防火墙的过滤而无法建立。为此有人发明了一种主动式FTP,即数据连接也是由客户端主动请求建立的,但是在服务器中接收数据连接的就不一定是20号端口了。

完形填空

The seven Cs of a good letter

What is the secret of writing a good letter? Here are two main ones. Don’t try to be complicted(复杂的). Don’t try to impress(留下深刻印象)your reader. You will be successful if you follow these seven Cs.

Clear. Use short, direct sentences.   小题1:  Just imagine that the reader is right there with you .Above all, don’t use an introduction.

Correct.     小题2:    Don’t guess, even for spelling. Refer to your dictionary. If you need to , check a reference(参考) book too. Use them as much as you need to.

Complete(完整的). Don’t scatter(使分散) our points.  小题3:   This is good organization too.

Courteous(礼貌的). Be friendly rather than overly casual. Present your information nicely even if you are complaining about something . In all letters, treat others as you want them to treat you.

Concise(简洁的). Make each point as clearly and briefly as you can.

Conversational(会话的). This is really the secret of good writing.    小题4: .  Such a letter has a natural, friendly tone(语气). Let your personality come through naturally.

Considerate(体贴的;考虑周到的).   小题5:  Write about what you believe the reader needs or wants to know. Try to be helpful. This will build good feeling towards you.

The seven Cs are about writing letters. But how about school papers? Use the seven Cs. Write as if you are talking to your teacher or professor. You’ll be surprised. You’ll almost instantly become a good writer. And you might even enjoy writing from now on.

Just “talk”to the person

Think of the readers’point of view as you write.

Make them easy to understand.

Include long sentences in your letter.

Make sure what you say is correct.

Writing should not be taken too seriously.

G. Finish one point completely before going on to the next.

单项选择题