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.服务捉供商

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。

计算题
阅读理解

Ever since news of widespread food recalls caused by a carcinogenic dye broke, there has been confusion(混淆) over possible links to the country of the same name, but Sudan officials say there is no connection whatever.

Sudan1 is a red industrial dye that has been found in some chilli powder, but was banned in food products across the European Union (EU) in July 2003.

Since the ban was put in place, EU officials have been striving to remove some food products from the shelves. So far 580 products have been recalled.

Last week Sudan’s Embassy in the United Kingdom asked the Food Standards Agency (FSA) for clarification of the origin of the dye’s name.

Omaima Mahmoud Al Sharief, a press official at Sudan’s Embassy in China, explained the purpose of the inquiry was to clear up any misunderstanding over links between the country and the poisonous dye.

  "We want to keep an eye on every detail and avoid any misunderstanding there," she said. "Our embassy to Britain asked them how the dye got that name and whether the dye had something to do with our country. But they told us there was no relationship."

The FSA, an independent food security watchdog in Britain, received a letter from the Sudanese embassy last week.

 "They asked us why the dye is named Sudan, however, we also do not know how it got the name," she said. "People found the dye in 1883 and gave it the name. Nobody knows the reason, and we cannot give any explanation before we find out."

Sudan dyes, which include Sudan1 to 4, are red dyes(颜料) used for colouring solvents(溶剂), oils, waxes, petrol, and shoe and floor polishes. They are classified as carcinogens by the International Agency for Research on Cancer.

小题1: What does the underlined word mean in paragraph one?

A.Causing cancer.

B.Having side effect.

C.Containing poison.

D.Poisonous.小题2:How did the Sudan1 get its name?

A.The dye is often produced in Sudan.

B.The dye has something to do with the country named Sudan.

C.Nobody is sure of the origin of the name.

D.Many foods produced in Sudan contain the dye.小题3:We can infer from the passage that.

A.the Sudan government is paying much attention to the food safety

B.Sudan1 is often used to be added to the food

C.people didn’t realize the danger of Sudan1 until 2003

D.many food shops will be closed down小题4:Which of the following is the best title?

A.Keep away from Sudan1

B.No Sudan1 dye links to the country

C.How Sudan1 dye got its name?

D.Pay attention to the food safety