问题 单项选择题

One ofthe main resposibilities of ICMP is to report(1).Although technology has produced increasingly relaible transmission media, errors still exist and must be handled. IP is an (2) protocol. This means that error checking and error control are not a concern of IP. ICMP was designed, in part, to compensate for this shortcoming. Howerver, ICMP does not (3) errors, it simply report them. Error correction is left to the higher-level potocols. Error messages are always sent to the original (4) because the only information available in the datagram about the route is the source and destination IP addresses. ICMP use the source IP address to sent the error massage to the source of the (5).

空白(2)处应选择()

A.reliable

B.unreliable

C.available

D.unavailable

答案

参考答案:A

解析:

ICMP的主要责任之一就是报告错误。虽然技术的发展产生了日益可靠的传输介质,但是错误仍然会出现,所以必须进行处理。IP是一个不可靠的协议。这意味着错误检查和错误控制与IP无关。ICMP的设计就是为了弥补这个缺陷。然而,ICMP并不纠正错误,只是报告错误。纠正错误的功能留给高层协议。错误报文总是被发送给源站,因为在数据报中有关路由的信息就是IP源地址和目标地址。ICMP使用源IP地址把错误报文发送给数据报的源结点。

填空题
阅读理解

阅读理解。

    Go to church, then have a big lunch, then go out to play while mum does the housework. That was a

typical (典型的) British Sunday in the 1960s. But things now could not be more different. 

    Some British sociologists recently studied the typical British Sunday. They found that people get up later

and do less housework than they did 40 years ago. They are far more likely to be out shopping or enjoying

themselves than cooking Sunday lunch. 

    Sunday mornings were busy 40 years ago. Most women caught up on their weekly housework and

cooked a nice lunch. They seldom allowed themselves any "leisure" until afternoon, after the dishes were

cleaned. Then there would be another rush to the table between 5:00 pm and 6:00 pm for tea. But now,

Britons can have brunch (早午餐) at the restaurant. Fewer people bother to cook themselves. "You only

have two free days a week. You don't want to have to waste one because there is nothing to do but watch

boring TV," said Elizabeth Biggs, 25, a producer in London. 

    "On Saturday you are recovering from the week," Biggs added. "Sundays are the last chance for the

weekend - you want to get as much as you can out of the day before you have to go back to work." In

the past, British women usually did their shopping during the week, while the husband was at work. "Now

men seem to do that as much as women," said Jonathan Gershuny, a professor who took part in the study.

    Men also do more housework now on Sundays. Back in the 1960s, men were far more likely to spend

Sundays out of the house at the pub or playing football before lunch.

1. Many Britons have brunch at the restaurant because ______. [ ]

A. They have no time to cook at home.

B. They get up too late.

C. They won't bother to cook themselves.

D. They will go to church.

2. Which of the following is NOT true? [ ]

A. Britons used to go to church on Sundays.

B. Britons usually had a big lunch at home.

C. British women usually did their shopping during the week in the past.

D. British men did little housework at home in the past.

3. The text mainly tells us ______. [ ]

A. what Britons did on Sundays

B. why Britons go shopping on Sundays

C. how Britons spend their holidays

D. the changes of the ways the Britons spend their Sundays

4. What can we infer from the passage? [ ]

A. Men do more housework on Sundays.

B. Sundays in Britain might be very boring in the past.

C. No people go to church on Sundays now.

D. Britons all go out on Sundays.